Affordable Used SLR Camera: Nikon D70s, Olympus E500/E510, Canon EOS 400D, Nikon D3100, Pentax K20

I will buy my first SLR, of course, used. I would like to fit in 700 zlotys, possibly a dozen or so zlotys more.
I looked at Allegro and OLX and there are many cameras at this price, but they are old and I do not know how many more they will work.

I selected:
Nikon D70s
Olympus E500 (set)
Olympus E510 (set)
Canon EOS 400D
Nikon D3100
Pentax K20.

What would you choose from it? I completely don't know SLRs, I don't want to get on my face.
It will be used for both studio and outdoor photos. And I would aim more for larger sets (unless there is a very good model)
Thanks for advice.

I would choose the EOS 40D with the first shutter and mileage up to 20,000. Many such cameras lay at the bottom of the trunk of wedding photographers in reserve. Kita can be bought for 100 zlotys so it's within range. It's worth looking for newer versions 18-55 because each next one was better. When it comes to failure rate, when buying a drug, you always have to reckon with it. It is good in Canon because it guarantees a shutter course and it is one of the most common problems besides disc failure.

At this price, you can easily buy a D80 + 18-70mm in a Nikon, which is a great set, a bit better than the very good Canon 40D mentioned here.
There is also a pretty cool Sony A33 from 18-55, much newer design and worth attention.