As said above, it is not difficult to obtain the socket 370 chips and use a slotket. You only need to take care that the slotket is reliable held in the slot.
But if you want to run them in dual cpu configuration, it's way trickier to get them run. Most slotket are not dual capable per se.
There are only a selected few, which are (also not cheap) and there are some, which can be modded for dual use.
Here, Tualatin celerons are not feasible, as there are not dual-capable. Anyway, on a dual Tualatin-capable board you'd probably invest in the best you can (the "kings"), anyway ...
So for the dual boards you pay the premium for avoiding to look for those rare slotkets or the time to modify the slotkets.