what are the best but not pricy crank for xc/mtb?

It is hard to beat Shimano's XT group. It is the closest to their XTR product line in quality, and weight, but hundreds of dollars less.

Hope this helps.

Depends what you mean by pricey, I guess. If you want to stay less than $100, there are several to choose from. The Shimano Deore LX and Truvativ Firex cranks are pretty decent, and the house-branded cranks at www.nashbar.com aren't bad either. If you want to spend a little more money you can get lots of great cranks from RaceFace (Evolve), Truvativ (Stylo), FSA...plenty of others.

If I were to pick one, I'd steer you toward the Truvativ Stylo. You can find closeout models for under $100 sometimes.....the new ones aren't that much more. They have very good chainrings, are comparable in weight to anything else out there below the elite race level, and my set has withstood an awful lot of abuse, torquing, and jumps. I also rode some Firex cranks for a little while and was pretty impressed with them for durability as well.

Since you didn't mention your budget I'll use my standard answer for cranks on a budget... FSA (Full Speed Ahead) is probably going to be your best value. Just choose a model that meets your needs and price.

They have a multitude of models from superlight and expensive carbon fiber units all the way down to utilitarian stuff.