Do you offer gluten free cakes? Do you have a favorite recipe you like to share or a favorite box mix brand? Do you charge more for GF cakes? Do they taste good? How stable are they (ie, can they hold up to the weight of fondant)?
I just do cakes for family and friends, but I do a lot of gluten free baking since I and many members of my family are on GF diets. GF baking is much easier to do these days than it once was. There are a lot of really good flour mixes and/or baking mixes out there that are yummy and easy to use. Decorating them is pretty much the same, they hold up well under fondant.
The local health food store is a good place to start. They have lots of gf flour mixes that you can use cup for cup subbing for wheat flour in your recipe. If you choose a flour mix to use in your recipe check to see if it has xanthum gum in it. It is necessary to keep the cake from being crumbly. If not, you can get it separately and add 1/2 tsp per cup of flour.
(I really like the Herseys chocolate cake recipe that comes on the back of the cocoa box. I add and extra 1/4 cup gf flour mix and 1tsp xanthum gum.)
Or there are box cake mixes. Betty Crocker now makes GF mixes and I also recommend pamela's brand. I can't really help you with pricing because I don't sell cakes currently but I can tell you that gf material will be more expensive(especially if you're buying boxed mixes) and they only make one 8" round instead of two.
When doing GF baking it is really important to be careful of cross contamination. Wash everything down really well to be sure there are no traces of flour or crumbs and be sure to bake on a day when you are not baking wheat items, (since the flour can hang in the air). Check all you ingredients to be sure they do not contain gluten, wheat, barley, rye, malt, of modified food starch.
Hope that helps, happy baking!
You may want to send a message to jasonkraft, He does allergy friendly cakes and may be able to help you with the pricing questions.