"A frog ascenders should cost you less than those for a Mitchell or Texas IMO (Texas uses 2 hand ascenders right?"
Actually, both systems use 2 ascenders, neither of which "have" to be handled. Which is why if you make your own system, both the Frog and Texas will cost you about the same.
"The frog harness should be no more difficult to make that a Mitchell harness and the chest harness is considerably easier as it isn't life supporting."
Right, the chest harness on the frog is not a life-support device. The chest harness on the Texas can be, although it depends on if you run your top ascender to your chest harness, sit harness, or both.
People don't stop and think though; the chest harness on the Mitchell Ropewalker is not really "Life Support" either, as long as you have your safety cords attached from your top ascender to your sit harness and your sit harness to your bottom ascender. So if your chest box or harness breaks, you’re automatically converted to a Texas sit-stand system. So on the Mitchell (unlike other ropewalkers) your sit harness and your chest harness are your life-support harness's, which means that if one fails, the other should convert to your life safety harness.
Another cool thing about the Mitchell is that if you add a bungee cord from the top ascender to the bottom ascender, you now have a Bungee Mitchell, where the top ascender pulls the bottom up automatically (when you release the weight from the bottom ascender, pretty much just like the Double Bungee Ropewalker.)