Last time when our dentist prescribed antibiotics he chose a $500+ pill, we went back and asked, and he changed it into something that cost less than $20, some times doctors are clueless about actual cost of medication... I looked up your prescription, generic version of doxycycline hyclate is only about $2 per 50mg pill, you could check with your doctor again if it's not too late..
http://www.drugs.com/price-guide/doxycycline