There may be options you haven't considered here.
I would first ask what your estimated sales volume would start at. Since you are new to online business the volume would most likely be small then grow with exposure.
If thats the case then not having to get a merchant account might be a better solution. With Yahoo you STILL have to gain a merchant account, and those fees are on TOP of yahoo's gateway processing fees.
As far as shopping cart software they are a dime a dozen and many great ones are offered free of charge like OScommerce (open source).
Many of the processing gateways offer them for free also so take a few moments and shop around.
What I would suggest is to find a gateway processor and talk one on one with a rep, they will ask a few questions to find out your EXACT needs and tailor a plan that suits both your business and your wallet :)
btw you can always utilize yahoos name appeal and link out to your site no matter where it is located.
I hope this helps some .. good luck!
