Hey man no offence but first off like everyone said, your never gonna be able to build even that arm you have sketches of for under $300. Secondly, i highly doubt anyone would be willing to put in the time to make schematics for your robot arm for you. And Thirdly, check out this forum post:http://www.societyofrobots.com/robotforum/index.php?topic=1335.0
This guy is actually working on a humanoid robot, Aiko. However, he also has spent $20,000+ on his project...and has years of programming experience.
But by all means if your up for it, try contacting him to get some advice.
I know your all hyped and want to build a robot and such, and so was I three months ago when i first discovered this site. But after reading tons of tutorials and the forums, i came back down to earth and realized for someone like me who had no previous experience with robotics, idd be better off to start with something simple and easy: the $50 robot. Even the $50 robot doesn't truly cost you $50...that is if your starting from nothing and have minimal experience with soldering etc. (like me). My $50 robot cost me well over $100 in the end due to all the Extra costs - helping hands (I couldn't have done my robot without them, you need em!), super glue (for servo modding), shipping fee's, new solding iron (my last one broke) and the list goes on.
Trust all the other SoR members (and me) who say this: Start with the $50 robot. Its both relatively inexpensive and a great learning experience. =)