I would also add that the 850/_70 are plagued with the inability to start up if you had just ran the engine for a brief period of time. This occurs because during startup, a LOT of fuel is dumped into the combustion chamber. If you don't run the car for long enough, the fuel isn't burned and essentially floods the engine. It dilutes the oil and causes a loss of compression. So if you are experiencing this problem after running the engine for a brief period of time, i.e. moving the car from the driveway to the garage, etc, it may not be able to start for 5-10 minutes.

Holland
It is possible that your problem is a component that has a defect aggravated by heat.
I had an '83 Malibu that had the same symptoms - all I can tell you is that a new starter did not cure the problem, a good mechanic never fount the problem, neither did I.
One thing that I would try is to get a hair dryer that has a "cold" setting and try to cool one component under the hood each time you get home, then try to start the car. Be careful what you touch when trying to do this, you could get burned. Electrical components would be my first suspects.
It is possible that you might find the offending piece. If you do get a result, that is, the car starts after you have cooled something, then you can try to repeat your success. If you can repeat the success, you have probably found the problem.
I realize that my suggestion is goofy, and most likely won't work, but the cost is right!