I have a couple of remarks

1 - Your malaria/ebola comparison must be off somewhere. Here's how I see it: Malaria - $5 to distribute a net, some small chance of preventing a person from getting malaria, some very small chance of fatality from malaria. ~$4k per life saved. Ebola - $10 to distribute a kit, some small chance of preventing a person from getting ebola, 50% fatality.

So the effectiveness of Ebola kits does not need to be anywhere near as effective at preventing infection in order to be equally effective. Ebola kits need only prevent infection ~0.2% of the time to be effective. Note - my calculation probably has some errors and omisions.

For reference, GiveWell's estimates, CDC projections

2 - CDC is modelling the no-intervention case as exponential, doubling every few weeks. Reading their paper might inform an intermediate-case growth trajectory

3 - It's worth considering how many millions are being poured into ebola reduction by national governments and thinking that if these governments are intervening effectively, then our inroads into ebola are likely to be proportionately smaller, according to the smaller size of our monetary contribution.

4 - A recent relevant link, HT Carl