It's kind of hard to tell, but it looks like a worker's coveralls type of clothing. Walmart sells lots of different kinds. Might even find some in store on clearance. I got some a few years ago for like $17 to do a Michael Myers costume on one of their clearance racks. You could check the local thrift stores just in case too and might get lucky and get a coverall super cheap.
Finding coveralls period is difficult. They're made durable on purpose and most guys are reluctant to turn loose to them when they know they'll have to buy another one. Like Frankie said above, check thrift stores and garage sales first because even on sale, they're pricey. You might luck out asking on a local 'buy nothing' group as well. One other inexpensive source (if long term durability isn't an issue for you) is something like this: https://www.webstaurantstore.com/white-disposable-microporous-coveralls-with-hood-xl/488MP400XL.html It's meant to be disposable so I wouldn't expect much in the way of durability. Then again, it's cheap and you can afford a few mistakes!