I'd like to have a screened in area under my existing deck. I considered a stamped concrete pad, but the slope to the left makes me apprehensive due to cost of leveling everything out. If I wanted to put in a deck, what should my approach be? I really just want it to be levelish with the stairs pad, which means about a foot or so on the left side. Can I tie the joists to the existing beams? Do I tie it into the foundation or do I use cement support blocks or dig down and put in additional 6x6? Do I put in a beam in the center? Area is about 9x9.

It would probably cost less and last a lot longer to put a small retaining wall around the downslope side and fill it in with 3/4 crushed gravel plus pavers. Then you could screen it in and not worry about it all rotting out from under you.
I like that too. railroad ties or concrete retainer blocks for the wall and then fill it with stone.
Very helpful suggestion. I didn't think about that. Is this type of installation more prone to rotting because of it being close to the ground? Also, is the reduced cost due primarily to labor or to labor? Thanks again!
Any deck close to the ground is going to rot faster due to more water and less air flow, even with “ground contact” pressure treated. Where I am the code won’t allow you to put wood within 6” of the ground at all.