Start with a 6u flightcase of your choice. Add two 1u Supermicro servers, each with mirrored RAID drives. In the top two units, add a rackmount monitor drawer with a KVM switch - these are ludicrously expensive new, but you can pick them up quite cheaply used. At the bottom of the rack, fit a basic 1u UPS, just a few hundred VA worth in case you get unplugged. In the remaining unit, fit two half rack audio interfaces to the front and a little line mixer or a broadcast failover switch to the back.
If you don't need stadium-gig levels of reliability, omit all the redundant kit and you can put together a decent setup for well over a grand.