If it is simply an overgrown beak, a good herp vet will be able to trim the excess off without a major procedure. If your tortoise has an overbite due to deformation of the jaw, it may be much more difficult to correct. Pricing for either will vary from vet to vet.
Assuming your tortoises just have overgrown beaks.
Things that contribute to overgrown beaks:
1. Feeding soft or finely chopped foods
2. Poor tortoise diet
3. Having a species more prone to this problem
A couple recommendations to help after you go to the vet:
1. Provide your tortoises with chunks of cuttlefish bone, (found in the bird section of any pet store, or at www.cuttleboneplus.com). Some tortoises will ignore them for months and than suddenly gnaw them to bits. In addition to keeping the beak short they provide calcium. I buy the largest ones I can, break off the hard back layer with pliers, and break them into pieces small enough for the tortoises to bit on, (2 inches by 2 inches).
2. Provide french fry size food. Sticks of grass, vegetation or vegetables allow the tortoises to exercise their choppers. Soft or diced foods doesn't.
3. Condition your tortoises to eat more natural / fiber rich vegetation. Overgrown beaks are encouraged by feeding mainly supermarket produce. There are plenty of sites on the web to learn about good tortoise plants for your species. Many tortoise keepers grow their own tortoise food in their backyards in a pesticide free environment. The links below are several steps better than supermarket produce. Finding plants that are specific to Desert tortoises will be even better.
Hope some of this is useful,
Happy turtling,
John
California Turtle & Tortoise Club: http://www.tortoise.org
Tortoise Trust: http://www.tortoisetrust.org/care/care.html
World Chelonian Trust Care: http://www.chelonia.org/care.htm
Tortoise Food: http://www.chelonia.org/Articles/nutrientanalysis.htm
Wild plants for Tortoises: http://www.tortoises.net/
Tlady's Tortoise Guide: http://www.tlady.clara.net/TortGuide/index.htm
Cactus as Tortoise Food: http://www.russiantortoise.org/cactus.htm
Turtle Cafe -
Edible Landscaping: http://www.turtlecafe.com/edl_edible_landscaping.pl
Grazing Mixes: http://www.turtlecafe.com/products.pl?CatID=9
Edible Flower Seeds: http://www.turtlecafe.com/products.pl?CatID=20
TurtleStuff.com -
Weeds/Wildflowers Seeds: http://www.turtlestuff.com/shop/index.php?shop=1&cart=92440&cat=23&PHPSESSID=b3e7f279874865ee743ebb27e85d9378
Forage/Enclosure Grasses: http://www.turtlestuff.com/shop/index.php?shop=1&cat=25&cart=92440
Tlady's Tortoise Seed Mix - http://www.tlady.clara.net/herbiseed.htm
Walkabout Farm's Quantum Series (No Seeds, just dry plants) - http://www.speakeasy.org/~dervish/herpnutrition/grasslandtortoises.htm