Amazon/Ebay stock levels

[Topknotch]

I want to intergrate a virtuemart 3 website so stock levels are also affected if someone buys from an ebay or amazon account.
I have looked into this and there appears to be a couple of options -
http://www.holbi.co.uk/
https://polishedgeek.com/services/joomla-e-commerce/joomla-ebay-integration
Now looking into them further they are incredibly expensive and want a monthly fee!
However looking into a Magento equivilant - http://www.magentocommerce.com/magento-connect/ebay-magento-integration-order-import-and-stock-level-synchronization-also-supports-amazon-rakuten-and-play-com.html it appears to be free !
My question is , are there no alternatives or do I have to use Magento although I prefer Virtuemart?
Thanks