It all depends on the kind of project you want to build, if you are thinking of creating your own coin and launching it to the market,  then you should budget at least 3 BTC bought for developers and also payment of listing fee to exchanges so that your coin can be added to their exchange for trading, I am a developer and I have seen a lot of project been carried out,  the least they ever spent in making their success was 2.5btc.