there are several problems with cheaper servers:
1) they are generally unmanaged, meaning that if you don't know how to update your kernel or o/s or other software, you will likely get hacked eventually
2) they are generally unmonitored, so if your server crashes on a friday arvo of a long weekend when you have decided to finally take the time to visit your mum who does not have an internet connection...your server will stay offline till you return on Monday, you will have lost sales and your affiliates will get pissed off with you and may just leave your program
3) they generally use cogent or other non-teir1 bandwidth, meaning that they are slower and we all know slower pageloads results in more people clicking away out of frustration, plus of course this is their first impression on your site and if they find slow loading vids or pics then they will be less likely to join
4) cheaper servers really aren't that much cheaper