I hate to answer this kind of question. Because you’re gonna hate it.
A student and a professional are the same. A professional is always a student. You’re always learning something new. You don’t pay a developer cheaper rates because they’re fresh out of college. You gotta remember, it’s their job. Not buts about it. A job in this industry will always vary in the grand scheme of money, but paying for cheaper will get you the cheap result. The worst way to become competitive is to sell yourself below everyone else to make it look like “you’re cheaper, so choose you!” – doesn’t work like that.
Professionals are always learning. They’re students themselves. Regardless of the years of experience, after a year of learning CSS/HTML myself (Now my 7th year) I can safely say I’d charge you no less than that 20 year professional you’re talking about (and not because I’m arrogant about money, because I want to be able to afford to pay my bills!)
To add to that, you’re willing to pay another developer to do your work that you have been asked to do, as a developer? Seems like an unreasonable turn in profit (if any) doing it this way for such a small problem. Things could easily be fixed with bit of cleaning & brushing up of your CSS skills :)
If you must at all costs and it’s absolutely necessary, lookup freelancing websites such as FreelanceSwitch where you can post the job for a price and a munch of developers will ask to take up the job. Then you select who!