I am considering purchasing a home that has a problematic layout. I think I can solve the layout issue by moving the existing upstairs bathroom into the room next to it. I am an experienced diy'er, can sweat and move water lines, but no nothing of moving rough-in for toilet, tub and sink. Wondering if anyone knows how costly this would be? The existing stack pipe in the basement is about 6 feet from where I want to move the bathroom. Thanks

Without being on site we can't estimate a project so we don'[t try. However, I can tell you how a typical bathroom group roughs in. Most bathroom groups are roughed in like this.
Toilet connects to sewer main or the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim.
Let me know if this works for you. Tom