Another option might be simply running the cable down the wall, under the road (depending on it's makeup) and up the other wall. With the safe distance of ethernet being in excess of 50m it's probably the route I'd first take.
Also consider that joining to two networks together isn't as simple as connecting both switches.
I assume (given you have these switches in place already) that both also have WAN connections. As such you'll either need to remove one WAN connection and have all computers on the network use one of them, OR add a layer 3 switch OR get some routers capable of doing static routes.
Or something like that... it's been a while since I've looked into this as ultimately I just setup a VPN. With file sizes only ever really getting up to 2GB, and symmetric 150Mbps internet connections in both premises, we didn't really consider it worth the effort
A lot of the time robustness and simplicity is what people really want over something being super duper fast.
EDIT: Sorry, might have missed that you've got the kit already that you wanted