So... what's the best routing solution for..

OK. Lets see, you have a 75xx and you're plugging client Y into eth1 on
that beast. You're still worried about them having their own router?

Cisco 2514 is they want to throw some money around. Unix box with multiple
NICs if they want to be thrifty. No need for any RIP/OSPF/BGP. It's a
static route.