Hi,
as a experienced PHP programmer which is also known with the basic fields of webdevelopment I would like to work on this project.
The captcha error handling won't be a big problem. Let me see the code tell me how it should look and I will do.
Concerning SEO: I would do an on-page SEO as it is the first step for a good ranking.
My price includes also some improvements for your design. I tell you what I would change, ask you for your approval and then apply the changes. For further details pleas see PMB.
Regards,
extrawagant