Macs are great starter guns.
I would suggest an M11/9. Maybe I am not impartial since a M11/9 was my first C3 purchase. To answer all the naysayers, Yes it is a bullet-hose at 1000+ RPM, but goddamn is it fun. As cheap as 9MM ammo is I have absolutley no desire to slow it down. I just need to get a drum mag for it.
However they are still relativley affordable. If you look you can still break under the 1000 dollar mark.
They are acres of accessories for them. M11s are starting to become the 10/22s of the C3 world. Tons of accessories and parts availble.
Easy to work on for a novice with no shortage of NIW spare parts and High Cap magazines.
They are cheap to feed, reliable as hell and mine eats $89 case Wolf 9MM all day long.
I know that for my first machingun, the last thing I wanted was a slow rate of fire. Nothing puts a smile on your face by dumping 30+ rounds it under a second.
However, "budget" will no longer be part of your vocabulary once you get into this hobby as MGs have started to consume almost all of my disposable income. C3 is addictive as hell.