I was going to say "a Mexican restaurant". but then I remembered that "authentic" Mexican nachos always use that awful liquid cheese slop.
So actually, I would recommend a student bar, because there they will give you proper melted cheddar.
Or make them at home. purchase:
a bag of unflavoured nachos.
a block of cheddar
a load of cherry tomatoes
some chillis
an avocado or two
some sour cream
some beef/quorn mince
also salt and pepper to taste. maybe some vinegar for the salsa.