Ive been browsing and researching transferable MGs on the net and gun shows for some time now and the last time I saw a price nearly that low was back in 2014 or 15 on a 380 MAC 10 for about 4 grand. your probably not gonna find anything below 6 grand nowadays, if ya only got 3500 id suggest flipping it in Vegas or just settling with a bump stock or a binary trigger, I've put links below to the two least expensive MGs I've come across in a while in case you were interested, hope this helps.
https://otbfirearms.com/voere-model-2005-22lr/
https://www.gunbroker.com/item/770068268