If you have $800 to spend on this project I would go with the Maruzen APS series.
They are the top of the line BASRs, and from what I hear they give you great accuracy as well as consistency when upgraded, the two factors you want most in a airsoft sniper rifle.
However, it is pricey, and most likely you will use all of that $800 on the project, and alot of time making it work the way you want to. In the end however, you wont be sorry.