As long as it's in good shape I don't think you overpaid. Rocketeers are popular and tend to go higher than other vintage machines.
Accessories should be easy to find. I don't own a Rocketeer but IIRC they use slant shank accessories and black tophat cams like the 600 and 700 series Touch & Sews (if I'm wrong please correct me). Finding the accessories in an original box for your machine might take a little more looking. Sew-Classic sells slant shank feet or you can find them in the usual places like Ebay.
Rodney