First of all it is against the law for agents to discuss fees, as that could be considered price fixing.
Second commissions are negotiable.
Third in a cooperative listing typically the listing broker offers 1/2 there fee to the selling broker (so in your example above I believe you may of misunderstood what the agent told you)
Fourth - there are companies out there that will for a low set amount list your home on the mls. They offer the seller limited services and typically the seller would be responsible for showing the home, negotiating the home and if there is a buyer agent involved compensating that agent.
You dont have to offer compensation on a FSBO to the cooperating broker, but lets say the market price for your home is 100000 and you only have one buyer that came to you from a buyers agent, if you dont want to pay the buyers agent and lets use your fee above 3% and want the buyer to pay then your sales price should be 97000 problem is most lenders dont take fees into the equation seperately and many buyers dont have the additional funds to pay brokerage above the purchase price and that is why it is included in the sales price or in your case 100000 as the bank will loan them against it.