What would you replace these overhead ceiling fixtures with, without breaking the bank?

Situation: I have 3 overhead fluorescent lighting fixtures in my kitchen (original to my 1980's era house) that I'd like to replace. They are recessed between the joists. **I'm not looking to undertake some big project that involves re-doing the entire ceiling. **

Does anyone have any recommendation for a type of fixture that could be installed in its place? Would like something simple and plain and unobtrusive. I prefer something that just blends in, rather than drawing attention to itself.

The rough opening is 11 9/16" wide by 48 1/4" long, with a finish opening of 11 9/16" X 48 1/4" , so there's a lip running around the opening that a plastic sheet is supposed to fit into, but they always break when I try to place them in the opening (hence why I want to replace the fixtures.) Sheesh, I would just settle for finding some plastic sheet covers that don't break, if anyone has had this problem and found a solution.

Thanks!