Bookshelf speakers
AV123 is risk free on their bookshelf speakers and Aperion offers the same for all their models. AV123, SVS, Ascend, and Aperion all have some good options in the $300/pair range. I recently added the AV123 ELT525 speakers to my system for the surround channels. They are a compact monitor that sound good and look great, especially for $300/pair. For $4-500/pair you have some higher end options including the entry level Usher bookshelf speakers.
I started my system with a nice pair of bookshelf speakers, the Onix Ref 1's for about $500 used and gradually added an SVS sub, Ref 100 center, ELT525 surrounds, and an Emotiva amp.
SVS and HSU are good options for the sub.
If you are spending $400 for bookshelf speaker and $400 for the sub + shipping, you could buy the EMP floorstander 5.1 system that is onsale for $900 shipped.