I agree that the price doesnt matter as long as you are fullfilling your niches you are advertising and also how far you want to go in impressing the surfer (your members). You can also pick up package deals from content providers that offer you different niches to better help you a a site owner to fullfill all your sites. Here is one for example:
http://www.greenguysboard.com/board/...ad.php?t=17966
If you have any questions or help on niches contact me my line is always open.