The guys that have put in here have as many or more years than I do, but I will impart what I have learned to you.
If its plastic, it will break.
If its metal, it will break.
If it says Airsoft, 6mm, China, or Japan on it, it will break.
What you are really buying are the externals. Meaning the body style and construction materials of the external portion of the gun. The internals are inexpensive to replace when worn or broken and upgrades are fairly easy to install with some practice. If you screw it up there are people here that can help you or you can ask at DP.
There is no "norm" when it comes quality. Some (not all) of your mid level guns ($250-$450) have wonderful externals and are well put together internally. But, if you are on a short budget the bang for the buck will be the metal AK47/74.
Evike has the Dboys RK05 listed at $130. After 20% coupon and 3 day UPS shipping its $119.88. Kiley and I both have one (same model, RK05), as do others here have a Dboys (Kiley also has an RK01 and an RK02. Ulti has an RK10. Jed has an RK10 and an RK06 just to mention a few). They are a solid, well put together, workhorse.
http://www.evike.com/product_info.php?products_id=30093Note: the plastic CYMA CM028S at $117.95 is $112.52 shipped from Evike. Metal Dboys over a plastic CYMA for 6 and a half bucks more.