Have been doing this for a number of years now, and although someone said it works out as costly - it works out better than no booking at all, on the scale of what you take in it is worth every penny, so ignore that.
Under the new credit card regulations that came in this year, i find it hard to believe that you can simply set it up - with your web designer, maybe last year, but not this one - you have to remem that with all the card fraud that is going on people are more wary, and not so keen to put their card details in - so a recognised setup is security for the customer, and makes it a better looking operation.
I am in the process of changing mine over to a better system, and should be sorted in the next week or so, also someone said that would people actually book online when they are already on holiday. answer is yes, without a doubt.
If you want the details of the 2 companies i use email me at firstname.lastname@example.org
Off the top of my head, i would say it works out about 3.5 % of the total price entered by the customer, you will have to have a visa/credit card machine and have 2 seperate merchant accounts.