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.
XL BGE (#2) & Performer Platinum
Former owner: Jambo Backyard, Klose BYC, Lonestar Vertical offset w/ Insulated Firebox, Medium Spicewine, Pitts & Spitts, XL BGE (#1) & (2) Medium BGE's, 22" WSM & (2) 18" WSM's, 18" & 22" Weber Kettles