I had the odd thought that if there are youth racing clubs for cyclists in your area, you might be able to get a used bike when someone outgrows it.

You might wish to ask for a measuring, to have a good idea of the basic frame size you need, then put out a want-ad on Craigslist. The right frame might come built as the wrong bike, but parts are replaceable.

I have had very good luck putting the word out.

My mechanic doesn't mind that I get my frames used and do basic repairs myself, because I respect him enough to do my other shopping with him.