I have a bunch of the midi solutions boxes… but they aint cheap. fixing any one midi problem is $50.
A motu micro express, the 4 port version of the express xt should run you $60-$100 used though.
install the drivers and clockwork software on your computer, then connect the box, make the routings you want in clockworks. Then take it off the computer and you are ready to go standalone.
I have both the micro express, an express xt and also recently added an iconnectMIDI4+. its way more capable in filtering and mapping than the older used motu stuff… but of course, more expensive, but at $200 new its a relative bargain