I explored this pricing phenomenon when I bought a new pair of first stages.
What I found was that the retail prices for SP yoke and DIN first stages varied slightly with the cost of the first stage with a greater difference on expensive first stages than inexpensive first stages:
MK 25T Yoke, DIN = $93.00 difference
MK 25 Yoke, DIN = $43.00 difference
MK 17 Yoke, DIN = $28.00 difference
MK 2 Yoke, DIN = $25.00 difference
But the first stage prices alone are pretty misleading as you get a much better deal on reg packages. For example:
Mk 25 S600 Yoke, MK 25 S600 DIN, = $22.00 (rather than $43.00)
With the exception of the MK 25T, it is approximately $20 to $40 cheaper to buy the DIN version rather than to buy a yoke version and a separate DIN kit, at least through a US SP dealer.
So while the DIN variants are slightly more expensive, I think it mostly reflects increased production costs for the DIN attachment and, especially on the packages or on a MK 2 or even a Mk 17, the increased cost is quite reasonable and represents a substantial savings over buying a separate DIN kit.
In my case I bought a pair of Mk 17 DIN first stages rather than buy them as yoke regs and convert them with DIN kits as it saved me about $30.00 per first stage and I had no need for more left over yokes, knobs, and retainers.
In my opinion the DIN to yoke adapter is a pain as it extends the reg another 1/2 to 3/4 inch out from the valve. If the destination does not have convertible DIN/K valves, then converting the reg to a yoke configuration before going on the trip is in my opinion a better way to go. Your local dive shop should be abel to swap the parts for you during a pre-trip flow test for a reasonable labor charge.
I am pretty sure that you could get a yoke, retainer and knob for less than a DIN kit, but the end cost of a DIN reg and the yoke conversion parts would be comparable to just buying a yoke reg and a DIN kit when and if you ever need it. Either way, it's a lot cheaper than buying a DIN reg and then paying $60 or so for a DIN to yoke adapter that will press the reg into the back of your head throughout your trip.
In short, unless you need DIN, it makes more sense to just stay with yoke regs, especially for recreational divers who frequent resorts where DIN valves are not available - and that would be why so few DIN regs are sold in the US.
