If you absolutely need the feature set included with Magento, it is a great & powerful ecommerce plattform. Please note for best performance it is best to use a server environment optimized specifically for Magento. **as a side note, eBay has acquired Magento this week and according to Magento they will continue to operate as usual. http://www.magentocommerce.com/blog/comments/ebay-agrees-to-acquire-magento/
Well I will not suggest you to go for FREE (Open Source) Shopping Cart Software (if you are not a developer), because in start it will not cost you but later on you need to pay good amount for making changes and stuff like that... And If you know the development then go for Magento...
I am on OpenCart's side, it is a great software, very easy to handle with minimum issues and yes you can configure PAYPAL for free in it.
There are lots of free shopping carts out there or try to check magentocommerce.com. Or try to check ours we got some free stuff and great products. Cheers!
Try OSCommerce shopping cart. It's free and well working with paypal and many more online payment processing sites.
1. osCommerce if you have a low budget and want to use existing contribution. 2. Zen-cart is template integration is the main concern.Also security wise its much better then osCommerce( with oscommerce 2.3.1 security is improved). 3. Magento : This is ultimate but needs a better server and higher development cost( If your budget is above 1500 USd atleast).
Magento is also a great software but it is a bit difficult to handle for those who are not from development/programming field.