Firstly, does your MUD exist in text for at mo cos we have had people on here who have been converting the text representation into graphics by script.

If not then I would suggest looking at a VTT but then I would cos I write one. The point is that a VTT is a shared online collaborative mapping exercise. Ok so normally its the DM thats doing the map bits adjustment and players change their character tokens but it does not have to be that way. You can collaboratively edit a map online. A VTT has a grid and some tokens and you can import tokens in to use.

I would start at looking at what you already have to use first tho.