Sod 2.5 GBit and go 4 times faster! Use a £120 10 GBit 4 port switch? MikroTik CRS305 1G 4S+IN Switch
It's SFP+ so you could save money on the 10 GbE over twisted pair and just use Twinax cables (expensive and short) or use Fibre SFP+ modules for not too much (4 pack for £65 ish brand new!)
You'll probably need to use Ebay for the NIC though. New SFP+ NICs are still expensive.