DON'T sell your tops OR give up !! You don't have to own a LA or use a LA to quilt your quilts. You just need to practice straight-line quilting and FMQ on YOUR machine. It just takes PRACTICE. I used to get frustrated too, I couldn't afford to pay a LA. I just kept practicing and now I quilt my own quilts. I won't win awards for elaborate machine quilting, but I continue to practice new designs.
Take a look at Leah Day's website and videos for inspiration - she does amazing work and does ALL her quilting on a Janome. No LA, no special equipment. She uses a Janome 6600 and a 7700. Also, check out Elizabeth Hartman at Oh Fransson! - she does a lot of modern quilting, but she has great straight-line designs and simple FMQ - all done on a home machine.
If your current machine is uncooperative, can you upgrade to one with a larger harp ? Janome, Viking, Pfaff and Babylock all have reasonably priced machines now that give more room for machine quilting. You'd have that cost back after just half a dozen quilts, compared to LA costs.
Hang in there and practice !! :)