You're taking the wrong approach to this. You buy shit guns, you end up wasting your money. The more you cheap out on a gun, the higher the chance you'll end up having to buy another new gun shortly after from the massive headache that cheap gun will be.
Word of advice: Don't cheap out.
Look into what 'low cost' (Cheap is a bad word, don't use it.) alternatives there are out there. KA M4's are an option for sure, tested and true. As well as their Thompsons.
Just wait 'til you get your age verification run through and hold on to your money. There are many guns available through private retail and on the classifieds that might fit your 'low cost' budget.