According to my son, foreman for a flatwork crew, you just nailed it lil_Blue_Ford!
The boss of the company I worked for was a firm believer in making sure the entire crew was better educated. There were several times that he took the whole crew to go through a course on certain kinds of concrete work and get us all certified. Of course, the end result was that any time I walk around and see concrete work failing, I look at it and know what they screwed up.
Shoot, even at $200 that's nearly worth it. I thought it would run near $1000 to bring a truck out.
I'll give the local ones a call and see what they actually charge. Maybe I'll frame out that patio in front of the doors after all.
Meanwhile, borrowed a rotary hammer and the concrete is only 3" thick! I honestly thought it was heavier duty. We've even had a complete engine block fall on it and it only left a little dent.
The area is marked out (we're going 4'x4') and we're renting the saw tomorrow.
Thank you gentlemen, you have reassured me I can make this work one way or another.
The cost of getting a mixer out depends on both the area you reside in and the amount of concrete you get on it. Locally, for anything under 5 yards you get hit with a small load charge in addition to a higher per-yard price (cubic yards). Anything over 5 yards is just a standard flat yardage charge (IIRC it's around $115 a yard over 5 yards for 4,000 lb mix). For less the short loads, they usually don't add any extra charge for high-early strength cement or higher PSI rated cement.
For exterior concrete you'll want a higher air content than for interior work. Interior you want a lower air content because it is protected from the weather and high air makes it hard to finish properly (smooth troweled). Exterior concrete needs more air to make it more resistant to freeze/thaw damage and the like, but here's the secret - unless you REQUEST an air content when you order, you just get whatever they put in it. Locally we've had more success ordering a higher air content (6-8%), you just have to ask for it (and we also had the equipment to test to make sure we were getting the right amount).
As to having the engine fall on it and barely making a dent, there are a couple things that could be a factor as to why that was the result. It could be a higher PSI concrete (you can get through most redi-mix companies concrete up to 10,000 psi), it could have a solid compacted stone base (we have successfully driven loaded concrete mixers on 4" thick concrete driveways that we poured which had a thick base of modified (2a) limestone under them, it could have been properly moisture cured (as long as moisture is present, concrete molecules will continue their process of hydrating and continue to harden - this results in concrete that is green or blue in the middle over the right amount of time), it could be old style concrete that did not have all the chemicals and water reducers that are used today (which tends to make a harder slab), or it could have been because someone coated the floor with a floor hardening agent. Or some combination of those factors.