The chain ring on my less expensive MTB is stripped and needs replaced. I was thinking about upgrading the crankset on my better MTB. Both are 8 spd Shimano, which isn't as readily available as 9 spd. I want to upgrade the good bike to XT and put the Alivio crankset on the cheaper bike. But, here is the problem...If I go with a 9 spd, I will need to change the deraillers too, and I don't exactly have the $ for such an upgrade.

Would I be better off trying to find a cheap 8 spd to put on the cheaper bike or wait until I can afford the upgrade for the other bike?