different people are put off by all the different merchant services, whether it is paypal, netbanx et al.
From your point of view paypal is possibly slightly higher expense, but it is only when you take a payment. So it certainly is the 'cheaper' option to start with, as there are no monthly fees.
In addition, it may be that you have no budget at all, but something like mrsite could be a bit of a let down, once you get going. Remember there are no 'free lunches' as such.
I would research some more through here and on Google to find out more about 'off-the-shelf' e-commerce sites. There are many e-commerce sites that you pay a low monthly fee for and offer most of what you might want and give you scalability.
You might end up spending so much time installing and then as your knowledge grows get a little frustrated that mrsite can't do x,y or z!!
And even specialised children products are possibly a highly competitive niche to get ranked high with search engines.
So you may have to spend money or alot of time obtaining a high ranking with the search engines, so you wouldn't want a cheap site that hinders your rankings. Or your conversions...and conversions are the key to any website.
Hope this is of some help and to be fair I have possibly answered more than you wanted
