All sites are limited to making offers below the maximum fee for their category. They can however drop their fee to any amount, so a Pro site could make offers for $40, but not $260.
Basic sites - These are newer sites maintained by part time bloggers. Likely to have more ads and outbound links. Limited social engagement.
Pro sites - These are professionally managed sites that are regularly updated with fresh content. Stronger social engagement.
Pro+ sites - These sites have verified they have over 25K monthly UVs using Google Analytics (coming soon).
The 'All Considered' options lets you receive offers from the selected quality tier without specifying a max budget.
A budget of at least $100 will attract offers from better sites, particularly if you're promoting well known brands.