I have an SRC Gen III G36KV which I bought from AW for £165 - I'm very happy with it. I have upgraded the inner barrel by swapping a 455mm CYMA AK barrel into it, inside a 260mm x 40mm suppressor. That has added about 6m horizontal range.
Something to be aware of is that AW ask SRC to supply them firing at close to 328FPS and to get this SRC swap out the M120 spring the gun was designed for and put a tiny hole in the side of the air nozzle. Which means that a) the internals, which in Gen III's are designed as "pre-upgraded", are way more robust than they need to be for the spring they come with; and b ) depending on your local site/s' FPS limits, if you want to make it more powerful, like close to 350, but risking going over that, all you need to do is replace the air nozzle, which costs just a few quid.
The hop rubber they come with isn't that good. I've tried a few alternatives I had lying around and found that the stock one from my Ares L1A1 works best (probably because it's so cold @mo) but I have a Firefly to try soon also. A blue Madbull would probably do the trick very well.
I can also recommend CYMA AK's, especially for woodland. Their range and accuracy is frankly astonishing compared to many other AEG's, considering how cheap they are. But I'd say they are only bombproof if you don't dismantle them yourself very much, until you know exactly what you are doing, because it's easy to knacker threads/holes which bolts and screws fit into.
As the others have said, get used to your primary before you think about a secondary. But if you have money burning a hole in your pocket, bear in mind that a machine pistol is going to bounce around in whatever holster you can find for it, when you're running, a lot more than a semi-auto pistol.