I am considering taking Ser.3 also (already have 7 and 63), who is your sponsor if you dont mind? I am preparing to get material from here: http://thectr.com/Series3/main.htm
http://www.stcusa.com/ look no further Dearborn is ok but I always fared better (and felt more comfortable when taking the exam) with materials from STC
I used Kaplan for 7 and 63, and it worked well for me. I'm presently using STC for the 55. The materials were provided by the company so I assume it's the good stuff!
you dont need a sponsor for a series 3. when i took it the test was about $80 and you could pass with a 70% maybe even lower. if you want a certificate get a CFA. some people think its useful and level 1 is pretty easy...2 and 3 are different.