20-30$ worth of olives should do to buy, at least, some Boosts. Boost your sailors, get 100 Vets on each Gunner and the rest on rookies and you will get better spread later on. Still, Spread will only tighten at around lvl 65-70.

Oh, and also remember: You will need 5 or 6 Engineers at Kaiser level to speed cap it. 

As stated boosts are the best thing to buy as you can't obtain these through normal game play (although you get them in item drop events). Whilst lower level you should be able to get up to 100 vets on sailors and experts will grow, particularly with km as you should have aa gunners.

So $20 will get 400 olives, if I was you I'd get 5 boosts (for you engies, I promise you this is the best place to put them), then you have 150 olives left, personally I'd get an andrea doria pbb as that will be a great grind breaker for your first line.

So well worth it if you are here for the long run and only crazy people who want 200 vets on sailors spend a fortune (although this can be achieved through becoming great at aa too).