Designing Kitchens and Bathrooms - Help with replacing bathroom floor and tub walls

I am needing some help as to how to replace a bathroom floor and also the tub walls. There is a hole the size of a basketball between the tub and toilet that you can actually see down to the basement. I have tried to contact several contractors, but they either don't show up or if they do, they want to charge around $5000. My house is a modular home, so it is not the usual construction. The bathroom is only 4' by 8 '. I have purchased all new items, such as toilet, vanity, faucets, ceramic tile, but just not sure how to get started. I think the cause of the rotted floor is the toilet overflowing and also the tub faucets. The tub walls are also rotting, but since the tub is only 4' long, I am going to stick with this and just wanting to replace the walls around it. I did buy a tub wall kit, but still not sure how to install, since the current walls are just paneling. Please help me get this done before winter. I am afraid that all kinds of critters will be joining me if I don't get this fixed, plus don't really want to heat the entire basement too.:eek: :confused:

Since you have a new toilet, don't be shy about removing the existing one. Pull the thing and then, with a sawz-all, cut along the floor joists past the last of the rotted out part and remove the rotted floor material. When you get this done, you should be left with a hole that has the edges fastened to floor joists with no support on the ends of the cut, from joist to joist. You probably won't find any blocking between the joists to follow, so just finish the cut from joist to joist where you need to. Some will advise you to try to split the middle of the joists so you can nail the new material to the joist and have the seam run down the middle of it. I like to cut along the edge of it so the existing floor that remains is nailed to a full width of joist. That makes it stronger. Then scab on some more framing to box out the area you just removed so you have something to nail the new section to. This method can also be used to repair the walls.