Pendraken is £4.95 for 30, (and Kallistra and Magister Militium are similar) looking at Ral Patha and 15mm.co.uk you can get 10 figures for £4.50. Obviously for a given base size you will need slightly fewer 15mm figures to fill it than 10mm.
I should have mentioned I'm in the US. At the time, I was able to find 15mm figures here, but would have to get 10mm from overseas, or from importers who already factored in the cost of international shipping into their prices. I don't remember what the numbers were at the time, but a quick check online and it looks like I can get Black Raven (from US) 15mm for about $0.40/figure, and 10mm Pendraken (from UK) for $0.30/figure before factoring in any shipping costs.
The 15mm figures at Ral Partha UK (former Demonworld) are far more expensive than most other brands.
I don't remember how the basing numbers worked out, but yes, I would have also needed a few more 10mm per unit to fill the bases.
I don't have anything against 10mm figures, per se. Just that they didn't make sense for my project & situation.