You may find that for weekly options on penny pilot stocks or for options to expire in less than two weeks, that the midpoint is close to fair value. Most options are too wide or the midpoint may not be "fair value." Closing prices are typically NBBO bid/ask average. I'm not as confident as you are that getting pricing data this way is as meaningful as you expect.
xandman suggested ivolatility. ivolatility is not a bad place to start. They do offer the data you are looking for and can likely suggest a service that is compatible.
http://www.ivolatility.com/data/historical_data2.html
good luck...Bob
Thanks.
1. Planning to use options that expire within 2 weeks, and
2. Willing to limit initial testing to say 200 stocks, picked from from SP 500 and NAS 100.
So, closing prices, with liberal slippage, should be decent for testing purposes. (Having spent number of years -- albeit 15 years ago -- working with system trading in futures, one's worst drawdown is always ahead, so back testing is just a starting point.)
Considering my stock and option data guidelines above, I suspect fairly clean data is available for maybe $2,000-$4,000, including many option months I will not use. The rub is more likely the quality and robustness of the back testing platform, including learning curves.
I'd also consider working with someone knowledgeable in this area, with extensive knowledge of a particular back testing platform.
BTW, the fact that option back testing platform, and/or data, are not readily available, makes me think it a worthwhile endeavor.