When quilting on a domestic machine, one of the biggest problems is squishing enough quilt under the machine's arm. You can get around this problem by quilting in sections. My favorite method is to split the batting into 3 pieces, remove the two side pieces of batting, then quilt just the center section first. This reduces the bulk that has to go under the machine arm. This book describes several different methods of preparing a quilt to make quilting on a domestic machine easier:
http://www.amazon.com/Marti-Michell-...dp/B0002J5GX0/
For a budget of $300, I agree with going to nearby dealerships and asking about used machines. You can get more machine for your money that way. What you are looking for is a machine with a strong motor that will be able to handle the thickness of a quilt sandwich (weak motors can get bogged down). Make up some quilt sandwiches to take along with you so you can test how well the machine sews on layers. You want a machine that has these features: ability to drop the feed dogs, ability to set stitch length to zero, a darning foot and/or hopping foot (for free motion quilting), and a walking foot for straight lines. A walking foot made specifically for the machine is better than a generic walking foot.