You're looking $750 - 1k for conversion.
You need to disassemble your 1354, and ship front 1/2 to
@NakedDucks - $50
He is going to drill and ream the case for the manual shifter, drill and tap for the detent and indicator switch - $100 (Need to pay for jigs, drill bits, ream, tap, cutting fluid, mistakes, time and profit)
He will then ship back to you. - $50
Included in his shipping will be: shifter, linkage, mounting bracket for shifter, floor boot, custom shaft to mount 1350 shift plate in 1354, o-ring and cover plate for back 1/2 including time & profit - $250 (Novak Conversion Jeep shifters run that much with aforementioned pieces)
You will need to source 1350 transfer case and disassemble for required parts - $150
While you have transfer case apart, replace chain - $100, bearings/seals, silicon and oil - $50.
Subtotal $750*
Labor if you don't do it yourself/tools & BEvERageS if you do - $250
Total $1k
*Yes, you might be able to source parts for less/reuse existing bearings/chain/seal but you need to think average customer. Going to wrecker to source 1350 isn't everyone's cup of tea.
$500 for the rack and pinion in case isn't unreasonable for machining effort/low volume (the other $250 is shifter/linkage/boot). You have to factor in warranty replacements and lost shipments.
I've built a bunch of custom parts for myself and I was fully aware that I couldn't sell them at cost, let alone profit. Most of my perspective customers have just as much fun as I do making the one off solutions, so wouldn't pay for mine. I like the idea, but Ranger owners are a tight fisted bunch and I fear OP is underestimating the cost/effort.