Actually forumnye engines are fine, and there are lots, but do I have to use them?
Say InstantCMS 2.* in conjunction with the payment (I think the script was worth about 3000 there is) a better solution than the forums. Besides a mini social network allows you to create your community and engage in correspondence on the website.
But the master-barin!
IPB and vBulletin devour a lot of resources. I like smf ( Russian community https://www.simplemachines.ru/
In addition, there are cheap hosting for this CMS 100sm.ru/index.html#image1-14
with stable server and good technical support (hosting).
P. S. If your project is interesting, will help with launch, promotion and personnel (if necessary in the early stages). contact through here