You could open an account with an FX broker like OANDA. I don't particularly endorse them or have any experience with them, good or otherwise, but they have existed for a while, and they are a well-known name.
You could use their brokering service to trade your CHF for EUR in the liquid market, in which case you would know that you're getting the best price available. I don't know what OANDA charges for maintaining such an account. It might be a monthly fee or commission-based. Since you're probably not interested in lightning-fast execution, but rather just in not being ripped off by your bank or credit card company, the most basic account would probably be fine.
OANDA also has a non-trading service that simply converts money in one currency in one account into a different currency in another account. They will quote you an exchange rate online and I'm betting it will be closer to the liquid price than other services, simply because FX trading is all they do all day. If you compare the live market price to their price and don't like what you see, you can always walk away.