Budget Speaker Recommendation?

At your stated price used I say the Quad 11L2 or Polk Audio LSi7. The small Polks are a really nice sounding speaker IMO.

CHeck out the Canton loudspeakers, excellent value for money budget speakers

This is my own ignorance, but if they are on a bookshelf (there would be about a foot clearance from the back of the speaker to the wall), does it matter if they are ported in the rear)?

it definitely matters if they're rear ported--i did a very similar search recently for a near-wall placement monitor and some very good speakers, such as psb and proac, didn't work in such configuration. for your budget, i'd find a used pair of rega r1 or rs1--they're indifferent to placement and forgiving of electronics. alternatively, focal cobalt (which i ended up with) or chorus; cantons are a good budget rec as well.

Rear ports are generally designed to be used away from rear wall.

BEst to avoid in general for bookshelfs. Front ported works best. Acoustic suspension will work also but will either sacrifice low end or tend to be much larger.