Honestly, I wouldn't recommend the M324. There isn't a whole lot you can do to it to make it better than its rather poor stock form. Personally, I'd just say get a new gun altogether. Assuming you're looking for a bolt-action rifle,
http://pointact.com/prod_JG366A_736_45.html and
http://pointact.com/prod_MB01_464_45.html are reportedly pretty good (for the price, at least). The first one I linked to is compatible with mags made for the Marui VSR-10. The second link has a link to compatible mags.
If you're not restricting yourself to bolt-actions, I'd suggest the CYMA GLOCK 18C AEP or a CYMA AK-47 or 74 from the same place I have links to above. The AKs will probably need new mags.
But frankly, you're not going to be able to play seriously with anything under $100 left in stock form. Chances are high that something in the box is going to need replacing. I'd strongly suggest saving up for a while.
And for the spoiled douchebag smartass out there who got his parents to buy a $1500 PTW because he whined enough, no, CYMA does not stand for Crap Your Money Away/Crap You Must Avoid anymore, unless you're referring to the $2.50 spring pistols that retailers desperately throw at you for free.
