The first few months are tough. I think it was Flash who suggested starting a 'kitty account'. Money put into it from fees received would then be used for required shop purchases. It will take a while to build the kitty account though. If you have the time, take shops with no purchase requirement. Banks, cell phone/wireless shops, apartments/new homes, phone shops, 'browse' shops, new cars, motorcycles, and audits come to mind. The fees then fund your kitty account, but will take 30-60 days, assuming you find and get the shops.
Fast-paying MSPs - Shoppers Inc, TrendSource, iMyst, CoRI, and Bestmark, are some who normally pay in less than a month. As for moving up to higher paying shops, keep shopping and keep your eyes open. There are higher paying shops, but if you're referring to fees and not reimbursement, $10-$20 is about average.