I think a custom cake is definitely the ah... frosting on the cake when it comes to putting a party over the top. However, if budget is an issue (when is it not?), buying a completly custom cake might not be a feasible option for you. No worries, with a little practice and a totally inexpensive marshmallow fondant (MMF) recipe, you can create designer cakes for as little as $5. Cheaper than a grocery store bakery and a little more meaningful as well!
1 16 oz bag of Jet Puff marshmallows
6+ TBS water
1 tsp flavoring if desired
2 lb bag of C&H powdered sugar
1 cup shortening
Hint: don't use off-brand or old ingredients for this one. Normally I am all about store brands, but this is the one of the few times it actually matters or else you will end up with a grainy product.
Put marshmallows in a microwavable bowl with 2 TBS water and desired flavoring. Heat in microwave for 30 second intervals until melted, stirring each time. Add 1.5 lbs of the powdered sugar to the bowl and stir until it is a sticky, gooey mess. Generously grease your hands and workspace with shortening and then put your sticky glob of sugar in the middle.
While kneading the mixture, add a little bit sugar at a time until you get a bread dough like consistency. I usually only ending up using 1.75 lbs of powdered sugar or less. Keep greasing your workspace and your fingers as the mixture begins to stick. If your mixture is too dry or not very elastic (you should be able to easily stretch it without tearing), add a tablespoon of water at a time and keep kneading. It should take about 8 minutes of kneading to dissolve all the bits of powdered sugar and to get a firm, elastic ball of fondant. You can use this recipe right away, but it's best if left to rest overnight.
To store the fondant, coat it in crisco, double wrap it in plastic wrap, and put it in a ziploc baggie with as much as the air squeezed out as possible. It stores quite nicely in the refridgerator for a couple of weeks. To color the fondant, just roll in a couple drops of food coloring (I use the gel kind with no problems). Have fun decorating your cakes! Remember, it's just like playdoh, but way better tasting. If something doesn't look right, just roll it up and try again. Patience and practice is the key.
p.s. If you would like to cover a cake in fondant but are not sure how, youtube has awesome tutorials! Check them out!