Firstly, resources are spent on freezing people, keeping them frozen and researching how to improve cryonics. There may be fringe benefits to this (for example, researching how to freeze people more efficiently might lead to improvements in cold chains, which would be pretty snazzy). There would certainly be real resource wastage.

How does this connect with the funding process of cryonics? When someone signs up and buys life insurance, they are eliminating consumption during their lifetime of the premiums and in effect investing it in the wider economy via the insurance company's investment in bonds etc; when they die and the insurance is cashed in for cryonics, some of it gets used on the process itself, but a lot goes into the trust fund where again it is invested in the wider economy. The trust fund uses the return for expenses like liquid nitrogen but it's supposed to be using only part of the return (so the endowment builds up and there's protection against disasters) and in any case, society's gain from the extra investment should exceed the fund's return (since why would anyone offer the fund investments on which they would take a loss and overpay the fund?). And this gain ought to compound over the long run.

So it seems to me that the main effect of cryonics on the economy is to increase long-term growth.