Find a local hobby shop and see what they carry parts for. This is a hobby and you'll need parts!
Also, if you're not terribly mechanical yet, you'll probably need help figuring out repairs for a little while. And when it's Friday night with a weekend of playing RC planned... you will break something minor, and the hobby shop won't necessarily have parts for either of those vehicles you mentioned.
Definitely see what they've got and see if you can spring a little extra cash to support them (if necessary! Sometimes local shops are cheaper than the Internet!!) and they'll be more likely to help you out when/if you have any trouble or need parts late on a Friday night.