It depends on the branch of Planned Parenthood whether or not they have a "bucket of condoms". But they usually provide condoms at a discount or free - just walk in and ask .
And it's not "bad etiquette" - remember, they're there because they care about protecting people's sexual health (however, it might be a bit rude if you just run in, grab the condoms, snarl and run out again ).
We have a bunch of threads about getting free condoms and other safer sex stuff:
However, if you truly can't afford to buy condoms, you may need to think about how you'll pay for other sexual healthcare needs, such as STD screening or emergency contraception should you need it.