PR doesnt mean as much as it used to, so you kind of have to judge the quality of the site yourself. How many backlinks does the site have, and where from? Is the site in your industry, and are the sites linking to it in the same industry?
How long does the $350 get you on there for, and on what page, how many other external links are on that page?
Those are just the main points to consider. A few years ago I managed to blag a link to a new site off a PR7 site, and it payed off. My site didnt jumpt to a PR6 or PR7 it went to a PR4 which, with my other sites linking to it is what id have expected anyway. But it got indexed a lot quicker and a lot deeper, some really deep pages were indexed within a week and appearing in the SERPs. But it was also a site in my industry, I got good anchor text and thats why it worked.
Dont just think
PR, thing relevancy, think how long your links going to be there, and think how long that sites going to maintain its 'authority'.
Hope that gives you a few things to think about
