Yahoo can be good for some merchants, but with you selling one product it might be overkill. Also keep in mind that yahoo changes for their electronic payment gateway that you must use (between .5% to 1.5%) on top of what the merchant account provider will charge you - either Paymentech or Chase or Cardservice. Any First Data company will support Yahoo's electronic payment gateway.
Have you considered just a smaller shopping cart and hosting it on your server? And then you can get your own merchant account with an electronic payment gateway (LinkPoint, Vesign's Payflow, Authorizenet.com).
LinkPoint is usually around $15-$30 a month with no transaction fees. Verisign is around $45-$60 with 1,000 free transactions, And Authorizenet.com is about $10-$30 a month with $.10 per tranaction. Authorizenet.com and Payflow charges for their recurring billing while LinkPoint does not.