They might seem a lot more expensive, but when you're looking to hire a new employee (an expense on the order of tens or hundreds of thousands of dollars), the difference between $75 and $500 to advertise the position isn't really that significant.
In addition to what csomar said, for a small business or someone looking to hire an independent contractor, I think many advertisers would consider $425 to be a huge difference. But, I think a lot of potential advertisers would consider $75 significant in the first place.
But for me, charging advertisers a significant fee is valuable to establish that they're serious about hiring. That's the rationale behind the fee structure on my site http://WheresTheRemote.com/ . To me, an advertiser paying a fee of something like 1x or 2x the hourly rate they're advertising (for an independent contractor or employee, respectively) is a token of their sincerity about wanting to hire and pay the rate they advertise, which the site requires them to include in the ad. Conversely, unwillingness to pay such a fee makes me concerned that they would just waste the time of the job seekers visiting my site and I don't want to publish the ad, since quality is an important goal for my project. Of course, having a decent amount of traffic would help establish the value proposition for advertisers to pay such a fee.
You are here assuming that this source will bring enough traffic to be your only source? Otherwise, you'll need to advertise in many sites and at that time the price makes a difference.
Similar great idea, but no new posts in almost a month.