Hey Greg!
Just like every other facet of life nowadays, money motivates, time is money, etc etc.... I have no problem paying 20-40 per rehearsal, if it is a means to an end, and there are gigs lined up. In those situations I think of it as an investment. After the first 1-2 gigs that investment is paid off, and hopefully you have the chemistry, dynamics, and repertoire to keep everything afloat.
Currently I have a few friends that I get together w/ weekly, and another established band that rehearses the week or two before the start of the season~ neither one requires money to practice, but in the past I've played with bands that pool gig money, roll it over and then pay a little out at rehearsals just so no one blows 'em off.