Hi Linda,
I recently had a need to research free hosting services and eventually found one that seemed much better than the alternatives, infinityfree.com. It allows 5GB of storage and should support the PHP and MySQL requirements of Xertes, although I have not had a chance to install it as my research was on DAMs. I would however be very interested to know if you are successful in installing Xertes there so please let me know your results if you decide to give it a try.
One thing to be aware of with these low-cost hosts is that these are typically introductory prices that renew after a year at a higher monthly rate (e.g. $10-14) so check the fine print before signing up.
Hope this helps,
Keith