For pricing plans such as you describe, these would be more "Job Packs" as opposed to membership options, as this is the feature currently available in JobRoller as you can see from the JobRoller admin demo
here.
There isn't currently a feature for different member types, however there are plans for this in a future release of JobRoller.
JobRoller, like all of our themes, requires its own instance of WordPress to run. The solution in your case, if you intended to keep your existing homepage, could be to install JobRoller in a subdirectory and create the links between them..
e.g.
www.yourdomain.com <== Your homepage
www.yourdomain.com/jobs < Your JobRoller installation