Good luck getting out of Vegas or Nashville under 1K when you are staying 3 nights. Both cites are ridiculously expensive right now. It is hard to go to a casual fast food joint and not spend $50.
Vegas: I'd look into a hotel downtown or even Ellis Island. Way cheaper rates, but off the strip. Both are easy uber rides to the strip if you wanted to go.
Nashville: Last time I went we stayed at Moxy which is close to Kid Rock's bar, great location, rooms were a little small. Normally we stay at the Hilton for rewards, but it is a little walk away from Broadway.
I'm staying two nights. I've changed my budget to $1500 due to the concert which will run me about 200 for a ticket and guessing a beer is 20 bucks. Plus some extra for gambling.
Two nights at Excalibur (15 minute walk to MGM Grand Garden Arena where the concert is) looks to be like 250 total for the two nights (that does include resort fees I believe).
So far flight 260, concert 200, hotel 250, about 60 for airport parking and maybe 50 for Lyft rides.
Leaves me 700 for food, booze, and some bets, plus souvenirs of course.
The zombie burlesque show looks interesting.