There's really no "right" amount that is the magic number for any show. Obviously we'd all love to have deep pockets that don't run dry, but one of the magical elements of theatre is that you can do it with $0.
In your case specifically it's tough to tell with the information you provided. Is this a 2,500 seat house or a 100 seat blackbox? Another big factor is time - how long until you open? There is a golden triangle of producing a show. There's good, fast, and cheap. Any show can be two of three, but can never be all three. The reason I ask about timeframe, now, is because if you've got six months - then you have a good chance to work a lot out, your show could be good and cheap, but it won't be fast. If you don't have a lot of time it can be good and fast, but it won't be cheap. And if you need it to be fast and cheap... well, sorry to be the bearer of bad news...