There are two types of payment, and the (approximate, general guidelines for the) standards for receiving each type of payment are different. One comes in the form of a training group or club providing support such as kit, training partners, subsidized healthcare, PT, and living arrangements, and maybe even a part time job. These athletes--who receive varying degrees of the afforementioned support depending on their accomplishments and agreement with their club, with the guys at the slower end of the scale probably not getting more than discounted shoes and travel to a few club races--are usually 13:40-14:45 5k/28:30-30:30 10k/2:16-2:25 marathon types. Having an athlete who runs time like this on the payroll would do very little good for the shoe companies; someone struggling to hit an OT qualifier is very unlikely to sell shoes, gear, PowerBars, etc. Any support these athletes are receiving is developmental, and should come from organizations--like USATF--or individuals--the Hansons-- interested in developing the sport. Ideally, these athletes will eventually become good enough that they will be able to graduate to the second type of payment.
The second type of payment is one that allows athletes to be full-time runners. It's money from an organization outside of the sport's governing body or club system being invested in an athlete for financial reasons. A guy who can compete with the top runners in Europe, be in contention at major marathons, qualify for Olympic teams and then make finals and compete for medals once there is likely to actually have some impact on Joe Jogger's purchasing preferences, and so it behooves shoe companies, apparell manufacturers, nutrition and fitness companies, and other similar organizations to pay these guys to perform well while endorsing their products. Runners who are both big name and high-level performers like Webb, Ritz, Meb, Deena, and Kennedy a few years ago will all likely be able to live and live well off their deals with shoe/apparell manufacturers alone. What matters to companies at this point, though, is not just performance, but also exposure. Webb and Ritz got tons of publicity in high school and thus have a great influence on a generation of runners; Deena and Meb are somewhat known in the mainstream after their marathon medals. Other runners, guys like the Torres brothers (and maybe Goucher these days?), women like Blake Russell, are able to be full-time runners due to their endorsement deals, but aren't worth the same amount as pitch(wo)men because either their performances are at a slightly lower level, or their exposure isn't as good, or both. A leap in performance or a really good publicist could push these runners into the upper strata of professionals. Times for those who are going to live and live well off their running seem to be 3:32/13:10/27:30/2:09 plus good exposure, and times for those who are merely full-time pros are probably about 3:35/13:25/28:10/2:13.
Two notes:
1) I don't know how coherent this was.
2)There are, of course, a third type of runner who is stuck somewhere in the middle, getting maybe a little bit of cash from a shoe company, or substantial discounts and subsidies, but still working either full- or part-time and running times in the 13:30s, mid-28s, or 2:17-range. (But the dichotomy makes it all simpler.)