Advice on purchasing a good commercial grade machine for making plush toys

I am a toy maker. i make sock monkeys, other sock creatures, as well as other plush toys. i am currently using a Singer Simple...the machine i bought 3 years ago when i started sewing, and it has been a great little work horse, but i am quickly outgrowing it's speed, and it is frustrating to have to re-thread every 10 minutes, because it catches or gets tangled. any advice on a commercial machine? i am looking for something that is pretty basic but a work horse. i need straight stitches, and zig zag...don't need computerized, 86 stitches or machine embroidery. straight and zig zag or serger...that's it. speed would be a must.
looking to spend around $500 give or take.
ANY advice??

You might consider a sailrite, checkou their website they have a lot of videos.  The lsz-1 will do a straigh stitch or zig zag.  I go mine for $850 from another online seller,  That is a bit over your price range.  Otherwise look at a Janome they are known as workhorses,I have the dc5100 which will run $599 but thye have more bsic models that get great reviews and are under 500.