For the types of rides you do (fun, exercise, transportation, and "weekend rides"), how important is walking around, not being on the bike, before you finish your ride?

SPD and Crank Brothers both use "recessed" cleats, eg they're kind of buried in a hole in the bottom of the shoe, while SPD-SL and all the road systems put the cleat under the bottom of the shoe, and they protrude downward:





The recessed cleats are much, much easier to walk in. But road pedals can be (but aren't necessarily) bigger and wider, and the shoes can be (but aren't necessarily) stiffer in the sole. Both of those attributes can make a clipless system more comfortable on long rides.

For your budget, Shimano A-520 pedals would be a good choice in the SPD system. I've got them on one of my bikes, and like them very much. That platform-like thing around the part that engages the cleat, means the force is distributed over a larger area of the foot, which helps them avoid "hot spots," or small areas of foot pain.