This is an extremely easy one. Most QRSS operators once built a 30m MEPT. There is an easy way to recycle those transmitters for 6m. With a converter circuit running a 40MHz oscillator, a 10.140MHz MEPT would be right away transmitting on 50.140MHz. Not too bad, I figure. A NE612 would probably be the easiest and cheapest way to get there this way.
Alternatively, a subharmonic mixer (two anti-parallel diodes) on a 20MHz oscillator would be even easier to build.
There are canned oscillators for 40MHz and 20MHz available, not to mention those cheap crystals.