A tinny in the 4.5 - 5.5m size is what you want. Any smaller and you'll be struggling offshore in any sizable chop. Any bigger and it becomes a difficult handling the boat on your own.
As for layout - centre/side consoles are better for fishing BUT you have no/little protection against spray and believe me having buckets of seawater thrown into your face is not fun! So if you're going to be heading out where there is a chance of choppy water keep that in mind
The Trailcrafts are excellent value 2nd hand and because they are built well you don't need to worry about bits falling off or breaking! You should be able to get one in the range mentioned in good nick for <$20K. If you're not full bottle on tinnies get someone to check over likely candidates and give you a report. It's money well spent!
Yes you can get glass in that price range but they'll be a lot older (which can mean higher maintenance/running costs), and if you're going to be bashing around creeks a lot I'd say stay clear. Glass doesn't take kindly to rocks/snags!