You ought to be fine with any 7-speed cassette from Performance or Nashbar. Their Shimano-compatible house brands are cheap-ish, and will work okay with your drivetrain. As for the chainrings, leave 'em alone, and replace just the cassette... Then take a ride. If the bike shifts okay and doesn't skip under load, you've taken care of the big problem.
Shimano Hyperglide chainrings have weird shaped teeth among the normal looking ones. Look carefully for hook-shaped ones... They're telltales that the chainring is worn out... But still, you'll get many years out of the chainrings... I've got two bikes with better than 65K miles on them. One's chainrings are just starting to wear down, the other's look new.
I bet your's are okay.
Just FYI, I have a 7-speed roadbike, an ooooold Trek. I get about 2,500 miles from a chain before I'd better replace it... Get into the habit of replacing the chain promptly, and you can get 20K, 30K from your cassette.