You may find an offset for $300 but a good one is less probable. Everyone has a different opinion of good though. For an offset, quality is in in large part in relation to quantity of steel... and steel costs $$.
try craigstlist too. sometimes you will find a great deal on a used pit.
Lonestar 24" Vertical offset w/ Insulated Firebox & Performer Platinum
Former owner: Jambo Backyard, Klose BYC, Med. Spicewine, Pitts & Spitts, XL & (2) Med. BGE's, 22" WSM & (2) 18" WSM's, 18" & 22" Weber Kettles