I held off on doing a build up until I had a really good idea off what I wanted from it. I used, owned a bunch of different guns and still have 4 aeg's including my project gun. I found it impossible to buy a high rof gun with high fps. High fps out of box is easy, high rof out of box hard to find and very pricey. Getting av'd proved way more trouble than it was worth for me. So when I went ahead with a full buildup I opted to go nuts. The result is an awesome gun that resembles no actual m4 but has great rof and high fps. I gamed her all last summer after destroying the piston in test fires and replacing it before the season with no other issues. My budget was similar to yours and I stayed within it but with a bit of help from a couple spare parts and some discounted parts from a local shop. Make sure you ask around about compatibility first and make sure you know how to use a dremel if you decide to go ahead with a build.