There are tons of used crawlers for sale. As stated above, it is popular, however most of us crawler guys usually have at least 4 or 5 rigs and we're always buying, selling, and trading. However, most of the crawlers go for more that what you're looking to spend. Also, tons of axials are for sale really cheap right now because all of the comp guys are going to motor over axle setups now or in the near future.
I would advise against the RTR axial. It is not the same rig as the kit only put together. It contains a lot of plastic parts, doesn't have a crawler motor in it, and the electronics aren't worth the salt in a piece of bread.
However, I help young guys get started whenever I can. If you type me up something with your age, how long you've been into RC's, what you've had, and that you want to get into crawling, and send me a PM, I promise I'll do my best to help you get a rig for your price range, and it will be a nice rig that you can show up at a competition with and have a nice start.