4 speed od or 5 speed
You can buy overdrive 833's for under $250. I have several, I paid $150 for a couple of them. Not a great gear spread, but they bolt in.
As for the Passon 5 speed, I think his waiting list is like a year out right now. And I see McLeod pushed the mopar version of their 5 speed back to next spring, it was slated for right about now.
As far as $4k goes, I don't think Passon's out of line at all. A TKO conversion will cost you more, and require floor mods. A T56 conversion will cost even more than that, and requires extensive floor mods. A bolt in $4k 5 speed is a pretty decent deal if you can lay your hands on one.
As far as the Dakota 5 speed, I just don't see doing that much work to end up with that transmission, regardless of how free the transmission is. An 833 OD would be much easier to install, and wouldn't end up being any worse than the Dak trans as far as street use.