How much to compensate an independant sales rep?

I recently started a small web design & development that caters to a very specific blue-collar industry niche. One thing I am considering doing is bringing onboard an independant sales rep to drive sales, since like many tech gurus, I’m more comfortable with programming than I am selling. Since the salesperson would be independant, they would be compensated via comission only.

The upfront web design package will be priced at around $3,100, with an additional montly fee of about $300. The monthly fee pays both for hosting, site maintaince, and an Internet marketing and advertising campaign. These are largely cookie-cutter sites designed using highly refined templates. This ought to reduce the sales cycle a bit (and hopefully make them easier to sell?) What percentage of each sale should I offer the sales rep? So I or shouldn’t I offer him/her a percentage of the monthly fees as well? If so, how long do I continue to pay the rep a cut of that monthly fee? Thanks!