Ethernet to fiber optic<-------->fiber optic to ethernet?

I administer a network for a small non-profit..... however i don't know enough about networking.

Lately we have been having internet speed problems and Im betting that it is because our network has 70 computers all connected via 10mbit hubs. My under-funded project is to swap the hubs for used 10/100 switches.

However... here is my problem... one of the hubs is in a building which is a little further then the rest of the network so whoever set this network up used two 3com SuperStack II PS Hub 40 hubs with "3com TCVR Fiber module" and ran a fiber optic cable to connect the remote building to the rest of the network.

Swapping the rest of the hubs with switches is pretty easy because everything else is wired with CAT5 Ethernet cable. My question is.. is there a way i can get rid of these slower (10mbit) Superstack hubs w/ fiber optic card ? For example, is there some cheap device which is a ethernet to fiber optic converter which i can place on each side of the fiber optic cables so i can use a regular switch without a fiber optic slot?

any other suggestions?

thanks

It might be cheaper to get Power over LAN or whatever, bridges. This would be a lot cheaper upfront than fiber. Fiber would be a safer bet, but seeing you have hubs, sounds like they can't afford the $500 to upgrade to 10/100/1000. newegg has free shipping on Dlink 24-port unmanaged gig-switches for $160. So, for $640, you could have ~90 gig ports on actual switches instead of crappy hubs.