Here is a little tidbit from my publishing & promoting seminar:
It is very important that you plan your marketing budget! Outline what you will do before and after your book is released. Research all of the possibilities and options you wish to pursue - advertising, review copies, materials, promotional travels, etc. Then determine how much money you can spend in each area. You may find that your ambitions exceed your budget, but better now than later! Readjust appropriately and then do everything you can to stick to your budget. It is easy to become overzealous and spend all of your profits before you've made a dime!