I DIY soylent. It's cheaper (<$5/day (1), ordering everything online in America), and I'm not at all enthused about some of the choices for the commercial product. Here's my spreadsheet. Nb. this was made just for personal use (a) for sourcing (which is boring, tedious, and time-consuming) and (b) to estimate the price per day. I haven't included things you'll need like scales, something to crush the tablets, a blender and, most importantly, choline, since I already had enough of lying around. I also add creatine, although it's not essential. Check the original ingredient list and update if you're planning on using it. Partake at your own risk, and definitely don't do it if you don't have enough of a background in chemistry to go from "I need x grams of sodium" to "I should include y grams of NaCl".

Process

1. Make a bag with the proper micronutrient blend (I go back and forth about including (and taking) nootropics, but this is when I'd add them. Except bacopa. Bacopa's super non-yummy and would ruin my food for the entire day). I usually make 12 or 16 days worth and add psyllium to make it 3 or 4 cups, which corresponds to putting in a quarter cup a day. Liquid micronutrients go in at make-time.

2. Put olive oil into blender.

3. Add micronutrients.

4. Turn on blender and add water (the blender isn't going to be a huge fan of blending so little)

5. Add maltodextrin and whey. Don't lollygag, because otherwise something... weird happens between the olive oil, water, and fiber and it turns into an inedible gelatinous mass. You don't need to rush, but be snappy.

6. Store in refrigerator. Drink when hungry (I prefer it cold.)

Pros

• Fast (it takes a bit of time to make the micro bag, but whipping up a batch takes around 2 minutes)

• Cheap

• More nutritionally complete than your diet (or anyone else's) probably is.

• Taste is satisfying

• Mental clarity (I've tried various approaches to eating over the years, some of them good, and soylent is by far the best in this regard)

• You don't have to choose what to eat

• No skill (or, more accurately, you need (rudimentary) chemistry instead of cooking. I suspect the average user here is much more likely to know the former)

• All your foodstuffs are delivered to your front door. This was especially important as a college student constrained by bus schedules = going to store costs takes 1.5 hours.

Cons

• Boring (which I personally consider a pro, but most people don't)

• It ferments after a while. About a day room temperature, several if you refrigerate (which you absolutely should).

• If you add too much water, it'll be unpleasantly runny. If you add too little, it'll be unpleasantly thick.

• High startup costs (~$1000)

• You don't get to choose what to eat

• If you mess up, you can either wind up with a complete deficiency or overdosing by a few orders of magnitude. The spreadsheet I've linked to is meant for sourcing, not making it. Check elsewhere for how much you should put in/completeness.

• Pain in the ass to clean the pitcher. Soap + soaking in water for a few hours works pretty well.

• There is a completely reasonable chance something goes disastrously wrong, I contract the jumping cold robbies or somesuch and die horribly. Obviously, I think there's a very low probability of that happening, but very smart people I trust (ie. other LWers) disagree.

Miscellaneous stuff

• The amount of water you should add varies by person. Some people prefer thick, bordering on pudding. Others prefer it thin like gruel. You'll probably have a few unpleasant batches before you figure out what's right for you.

• Most things are best bought online, but in my area, the olive oil is notably less expensive in grocery stores.

• I mentioned I don't have choline on the list. By all means, use my spreadsheet to source things, but for the love of Cthulu, check sources not me to make sure you're getting the right amounts of everything. I take no responsibility if you derp it up and wind up deficient or overdosing by two orders of magnitude (which is surprisingly easy).

• As soon as I can afford to (ie. when I graduate/get a job), I'm planning on switching to mealsquares. They do the same thing but better (nutrients from whole foods, have the flavonoids/anthocyanins things, easier, and reportedly taste better). However, according to back of the envelope, they cost 2.5-3x as much (2)

• Many of my ingredients come from Amazon. Use amazon smile (I support CFAR) and, apparently, if you go to amazon following one of Scott Alexander's affiliate links (of Slate Star Codex) and buy stuff within the next hour, 4-8% (or more) will go to him. (I'm unsure about my affiliate assertion, but it's the best I can come up with and I'm at least 50% sure it's correct).

• With one exception, literally everyone I've told about soylent immediately responds with some variation of "I couldn't ever give up real food" and completely dismisses it as a thing they might possibly do. This would explain why it's not more popular

• My current model: macronutrient composition doesn't really matter. Yes, there's some essential fats and it's quite bad to not have enough protein and there's better and worse fats (omega-3 vs trans) and better and worse carbs (based on glycemic index). But, beyond that, the focus on "low-carb" vs "low-fat" is beside the point. 1, 2

• I'd be willing to answer any questions that come up. I've been doing soylent for a little over a year now, and am a pretty big fan of it.

(1) I weigh about 75 kilos, mostly lean, am active, and am trying to add muscle. This all has implications in terms of how much protein I include; changing any of these factors changes how much protein you'll need changes how much it costs, likely in the downward direction. Notice that protein, by far, makes up the majority of the cost (~40%)

(2) If you assume $5/day soylent and 2000 calorie diet, then mealsquares, at $75/6 = $12.5 / day. However, soylent is (slightly) less than $5/day. More importantly, I eat significantly more than 2000 calories a day, and with DIY soylent, you can increase the number of calories with maltodextrin which is ludicrously cheap.