What is the lowest end switches that do layer-3 switching all ports are 10/100/1000?
3560s and 3750s are the lowest end switches that run IOS that are L3 capable. They come with 10/100/1000 ports.
Don't quote me but I believe the Cisco linksys SRW's are the cheapest, although crappy at best if you ask me.
A solid proved model would be a 3750, like a WS-C3750G-24T which is a gig 24 port switch that allows Layer 3 ip routing.