Most affordable is leave it alone. To do this remodel correctly, with the correctly waterproofed wet areas, is not going to be “budget”, even if you DIYed all by yourself. You will need to replace the window for sure. A window in a wet area is an invitation to rot. Unless it’s vinyl or fiberglass and integrated into the waterproofing system correctly. A limited space means limited options, as there are code required minimum spacing that must be followed.

You need to figure out what you actually are willing to spend to get what you want. 20K? 40K? 70K?

https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer

http://starcraftcustombuilders.com/bath.design.rules.htm#.Wt9D4a9OnYX

" I think I will put the bath/shower long the wall with the window (replace the window) and move the sink to the wall that the bath was on."

Moving plumbing will get the price moving north quickly..............

Can you post a 2D overhead view layout with your measurements, including the area that can’t move b/c of the pipes. Do you want to keep both doors?

Take note of what Sophie said above. It's quite likely better to leave it as is. A good reno will need more flexibility, and will be costly. If you do anything, a shower in place of the tub, though not to the corner, is your best option.