Contract casting is readily available - it will be much cheaper than the sculpting.
Costs are going to come down to the number of different figures - if you have variants they will be cheaper, and many of the WM figures use this already to change the look of figures slightly, which adds to the variety of the unit.
HE and Araby spears are quite uniform, but Empire Halberds have much more figure variety.
I think from a sculpting perspective, having the figures cast on strips won't make a lot of difference, as they are likely to be sculpted individually, then have some cast up, converted slightly, and made into a strip.
Time scales may depend more on the schedule of the sculptor rather than just the sculpting time. In the recent Pendraken Mongol release - the range was sculpted in a few months - with 15 or so packs, each with probably 3 different figures - though these shared a lot of horse dollies, and probably some bodies.