Don't bring cash. Don't exchange cash. Use an ATM.

All exchange places want to make money. It's not a case of them being greedy, it's simply business. Some claim to take no commission, but then their exchange rate is really bad. Others have a good exchange rate and a high commission.

Carrying lots of cash around is a bad idea. If you get robbed the money will be gone.

Please note that most people say credit cards should not be used as ATM cards. I've never done this myself, but from what I've heard it's a really bad idea. Get a debit card with a low cost for ATM use in Europe.

I always use my debit/ATM card to withdraw money from the local ATM before I leave the destination airport. Check with your bank/credit union to see what the fees are (many charge a small percent fee for foreign ATM transactions but many charge a flat fee) and also to tell them that you'll be traveling. Many people do take a couple $100 bills as an emergency stash but don't actually exchange them unless they run into problems.

As anyegr said, don't use your credit card to get cash (unless it's an emergency of course) as they charge you interest from the day you withdraw the cash rather than after you get the statement and have a chance to pay it off.

Ditto the above advice. I do bring some USD cash (because I'd never go with only one method of getting funds). But primarily use my debit card at a bank ATM machine to withdraw local currency.

Exchanging at home before you go pretty much universally is a more expensive.