What type of Engine do you have in your Olds? How many liters is it? Then I can start to help you with some estimates. I would not worry about the fact that Olds is 'no more' because, the mechanical parts are pretty much all the same for Olds, Buick and Chevy. We do have a scheduled maintenance section for Repairpal.com Just go to the Estimate section and choose Scheduled Maintenance under the service type and then choose the 30k , 45k etc.
I am well aware of the Dexcool issue and I am glad that you are too. How many miles do you have on your Olds? If is is under 50,000 you can pretty safely switch coolants, if and only if, you are willing to do 2-3 complete flushes of cooling system.
I have found less problems with the. The smaller 3.1 and 3.4 liters are really bad. I have seen many, many failures. I used to work at a shop where we serviced a fleet of over 600 Buick Century cars and the first thing that we always did was to flush out and replace the Dexcool and, this was brand new cars!
Your Olds should run fine on 87 regular. Actually, it is a Federal Law that all cars made for the US Market have to run fine on regular gas and pass Smog. That is why they have Knock Sensors to limit the Spark Advance.