There is one options for a 'one night' camping pass - Lawson Hill - other than that, there are very limited options for a one-night stay in or around Telluride.
All camping is set up (depending upon the campground - there are 4 different camp grounds) for arrival between June 11 or so until the end of festival, departing Monday June 20
you can buy a camping pass for the Mary E or Lawson campground, they are $70-75 per person, so probably not a great option for one night. Lawson permits people with single day festival passes to camp there, but you have to find a Lawson camping pass for each person in your group. Mary E campground (formerly Illium) requires a four day festival pass plus the Mary E campground pass.
The details of all of this can be found here:
https://bluegrass.com/telluride/plan-your-journey/campingThere may be options further out of town - Ridgway State Park, for example, is about 45 min-1 hour out - has a lot spots for camping. There are RV parks in Ouray where you might be able to put up a tent. There is also probably some dispersed BLM land but I don't believe it's all that close
And, whatever you do - DO NOT buy a ticket from StubHub (scalpers suck) or Craigslist (most like a scam and scammy scalpers suck)
Now that you are registered on this site - check out the ticket trading section in this forum - you must be logged in to see it. Getting a single day Thursday shouldn't be that tough - a Lawson camping pass will be more of a challenge - you may also want to show up in person Thursday morning and hang out by the ticket window for the fest by the post office - a lot of ticket trading going on there as well.
Good luck!