That is a pretty good guess. I tend to buy my stuff in bulk and at a good price. Costco has Mobil one for 23 bucks for 6 quarts and ocassionally I get better deals, like the Pep Boy deal one of our members found, less than $2.40 a quart. Any thing less than 4 bucks a quart is good in my book. Then I buy oil filters by the dozen at a Toyota dealer, about $4.50 including shipping. You will need a teflon washer for the bolt on the oil pan, about 50 cents. That is about it, except paper towels, WD-40 and of course the cost of the tools. Right now it cost me about $28 to change oil in my 2001 which has a 6 quart capacity.
For conventional oil I figure getting Castrol GTX for less than $1.40 a quart is pretty good, (I use this on my 2 older cars). Right now I have 2 cases of Castrol and 8 quarts of Mobil one sitting around. Oh yes, I tend to pick a non-wet day and hopefully semi-warm before I change oil, but sometimes I have to do it on a terrible day.