Too much. Do it the right way. Dig a hole and pour some concrete
All you need is a sledgehammer to get the pins started, and a jackhammer with DP bit (which the store may loan you). Since my soil is relatively soft, I was able to drive these with a jackhammer I bought for $150. The DP bit didn't work for that jackhammer, but I found someone to weld washers onto one of the bits that came with it and used that. It helps to have two people when installing, one to drive the pins and the other to help place the DP in the beginning and make sure it doesn't rotate when you first start driving the pins.
To determine how far you will be from your house, set the DP on the ground and put the 4 pins in the slots without driving them. How far from the house they are when above ground, will be the same as how how far they'll be from the house once driven in the same spot. But remember if you rotate the pier, that will change the distance. I think Code requires a 6" buffer zone also.
Call your local building inspection department to see if they allow the use of Diamond Piers. Then use Trex's free deck design website to draw up code-compliant plans. The software will indicate how many piers you need and where they should be placed. Submit the plan to request a building permit, indicating you're planning to use DP-50's or 75's as the case may be. I used DP-50's except for one pier that provides support for a roof overhang. The inspector suggested a DP-75 for that one.
That probably wouldn't meeting local building codes. They really want at least a complete frost wall for a sunroom.
DP75 w/63" pins (1003-882-447) DP50 w/50" pins (1003-800-715)