Elance is notorious for underbidding projects. I have an account on it and submitted zero bids because of that. You just can't compete with it if you know what you are doing.
I have been doing software engineering for 15-20 years (depending on whether you count my co-ops or not ;) ) and have been in the application security space for the last 9 (wow).
Here's some tips:
If the contractor is suggesting you change to a different framework and their reason is: because we know it. Then you are probably getting screwed over. It is just a hunch. If they can offer some solid performance reasons (either site performance or lower development costs than continuing down the current path), they will provide that in detail.
Depending on the site, please make sure that you develop it (or your contractor/consultant) build security in (as I said, I'm in application security). I would be more than happy to discuss anything with you over PM if you have specific questions. I'm familiar with PHP, Python, Java, Perl, Ruby (very lightly). Feel free to reach out.