if you want no watermark you have to pay. the good news is, there's a student version available for about $400 (currently also includes free upgrade to Maya 8). As far as i know, the student license is exactly the same as the production license that you buy for ~6000. But you cannot use the student license for commercial work, unless you want to pay a massive fine. The student version has the functionality of Maya Unlimited. You can find it at https://www.studica.com/alias