English translations are very expensive. The only thing I can recommend is getting family from Iran to send it to you.
I have seen the Shahnameh on Amazon.com, but it's 3 books and each book is about 3 times what you're willing to pay.
I bought it off eBay a long time ago for about $30 brand new, and it is a very good quality book, and it was shipped from Tehran. I just searched for it and found 1 copy for sale but it's used and not from Iran. if you don't find it you might want to check eBay later. Search for "Ferdowsi" and "Shahnameh" because sometimes they don't put both words or spell it differently.