Surround quality depends on what exactly you are looking for. They are less important, but if you spend a decent amount of time listening to multichannel music for example, then you will want better ones. At $100 and less than 4" I think you are going to have a tough time getting even a decent quality speaker to meet both of those criteria.
Keep an eye out for the Polk R150. They can be had for around $40-$50, but I don't think they will meet your 4" requirement.