Wow, you've received some great suggestions I hadn't considered when I was in the market for a new machine! The vintage machines, Goodwill, church community are great places to look.
I guess it really depends on where your priorities lie. Is your budget pretty firm? Maximum harp size? Straight stitch vs 100+ stitches?
My first machine was a Brother CS-6000i off Amazon for $125. For the price point I can't say enough good things about this little guy. It was used a lot for three years before I added a PQ-1500SL to the fleet. Even though the 1500 was 5X the price, I still bust out the 6000i occasionally as it does a better job at some things than the 1500.
Yes, it has a small harp at about 5". If you're really looking to get into FMQ it will be challenging, but do able. I've quilted 60" square quilts on the 6000i, just go slowly, it works just fine. If you mostly just stitch in the ditch, the larger harp space is a little less crucial. The stitch quality is every bit as good as the 1500. If you're more into lap quilts, it should be even better.
If your budget it more flexible, cost and harp space tend to go up hand in hand. The 6000i had everything i needed to get started quilting until I progressed to a point that I knew what features I really wanted in my next machine (and was able to save for it!)
If I can make some assumptions, you sound like you're in the phase of life I'm in. I'm busy with my family, we don't have a ton of extra cash lying around, and I just wanted to get started sewing. Best of luck in your search!