This is kind of unanswerable, because a server lease completely depends on the application. Also, price shouldn't be in the list, because it's always the major factor, and it doesn't make sense to get a machine that doesn't meet your requirements just because of price. Price belongs in a datacenter-oriented list like "reliability, support, price, etc".
If I just need a file server, then the most important factor is going to be bandwidth. A low end celeron CPU and 512MB of memory in your standard starter packages would be fine. Possibly the hard drive would become a major factor, depending on the nature of the application.
If I need a server to host a couple hundred standard websites, then I'd take the smaller processor, a memory upgrade, and call it good. Bandwidth is not an issue, CPU is not much of an issue.
If I need a server to host dynamic sites, some of which may grow large, then I'll be looking at CPU, memory, and bandwidth, and then possibly hard drive.
In each of these examples I want to pay a low price. I wouldn't pay a higher price just because the price was higher. I wouldn't pay a lower price for a server that wouldn't handle the load.
The most important issues for us and in the following order would be:
1) Network stability and reliability
2) Availability of Support
3) Quality of Support reponses and solutions
4) Quality of hardware
5) Hardware replacement parts in stock and available for immediate replacement
6) Datacenter reputation
I see. I would be willing to bet most people look for bandwidth first in a low end server. I would expect a minimum of 500GB. One thing that bothers me personally when shopping for a low end, is that some are still being offered with 128 and 256MB of RAM....I look for a minimum of 512. A 1.7GHz Celeron processor or better is expected. And a 60-80GB 7200RPM IDE hard drive. Price-wise I'd want to be looking at under $120 with just a basic linux install.
It wouldnt need to be a ton of bw anything above 300-400gig would be reasonable for a 2 figure price, but what really bugs me is when I see providers selling high spec server with low traffic, when there is little for the machine to be stressed with such a limitation on traffic.