If you watch around, you can find deals on oil. Example: This month Advance Auto Parts has Mobil 1 oil (5 qt jug), Mobil 1 oil filter, and a roll of paper shop towels for ~$13.00 after rebate from Mobil. In store purchase only. You can do 2 rebates on this deal.
Another rebate oil deal that is running now is Pennzoil has a $10.00 rebate on 5 qts or jug of their synthetic motor oil too. You need to check on line but the big oil manufactures are always having rebate deals on oil.
The rebates are easy to do because there is nothing to send in. Just go to their web site, fill out the information for the rebate, attach a scan or photo of your invoice, and click send. I have received every rebate I have applied for, just read what is required and if questions, you can call them. I have gotten full synthetic motor oil for as little as $1.00 a qt after rebates. If I find synthetic oil for around $15.00 for 5 quarts after rebate, I buy it and stock up.
Note: These cheap synthetic motor oil deals are because the oils are not "true" synthetic. For a "true" synthetic motor oil, you would have to pay around $10.00 and up per quart. America has lower standards for what is called "synthetic". Search the web for more info.