I used to keep mine in 2 large Xpens in the dining room when I was having a lot of trouble with chewing and pottying in the house. It was a nice large area, with beds, toys, food, ect so they were perfectly happy in there when I was too busy to play.
I know that when we just put a fence up, we did it mostly ourselves so we saved quite a lot. Not sure if that is an option for you. It doesn't look the greatest because we hired a crooked carpenter at the end who did a "crooked" job on the rest of the fence, but it's functional and we paid I think around 2,000 for materials not including concrete.
Also, I know that the wooden fence panels at Home Depot and Lowes are cheaper then the Vinyl and still look really nice! Plus they are easier to put up because you don't have to drill the pannels into the posts... Just a thought
Or possibly could you get two big superyards or xpens and leave them outside as a fence that you can go out there with them and supervise, but then all can run around and potty at once?
Before my fence was up I used long tie outs, distanced from each other attached to their harnesses so they could all potty at once. I also did the Xpen thing I mentioned above.
To keep my house clean, I was their bedding daily. I vaccum my home daily and my couch weekly. I run air purifiers and get yankee candle plug ins to make the house smell nice. Also, any accidents and I use Natures Miracle pet cleaner. It's great to get the odor out of accident spots and you can also use it in the wash with their bedding.
It takes a little more creativity without a fence, but I think you can do it! Also... if the other solutions are too pricey you could look into making a temporary chicken wire fence for a smaller area.