I always recommend getting a dot com for your job board business. .COM domains are the most trusted type of domain extension so skip the .net, .co etc when it comes to establishing your site.
Many .com domains are already taken but there are ways to find and acquire a good one for your job board.
My two favorite places are GoDaddy Auctions and SEDO. They offer the best opportunity to get a good domain for your job board.
Sedo is a marketplace and you can find a lot of good job domains. Generally speaking most of these domains can be had for between $1k and $10k. Those are fair prices for a decent two word domain right now.
Just type your keyword and choose the .com extension to do a search.
On GoDaddy one of the services they have is a concierge service. If a domain you like is taken you can pay $99 to have them contact the owner and negotiate on your behalf based on your budget. I have used this service before and its great. A GoDaddy rep will call you to discuss before the initial outreach.
As a best practice I keep all my domains on Godaddy separate from any hosting company. Just makes my life easier.