Honest question about stretch goals... How much extra will those cost, though? 
Each mould costs me ~£150 to set up and generate the first set of spins with the company I'll be using.
So two pledges for a total of £120 means that although I won't have broken even, at least if I never sell any more models I won't be making a *huge* loss.
As to the actual cost of the final models themselves for the stretch goals, I'd estimate their sale prices as:
- Lesser Goblins - 10 strips of Lesser Goblins, 2 strips of Lesser Goblins with command group - £10
- Large Cannon & Large Catapult, dragged by Woolly Rhinos - 2 War Machines - £12
- Monstrous Woolly Mammoth + Ogre Riders (Commander & Wizard rider options) - £10
The Goblin strips will be 40mm wide. Could have them small enough to fit 3 deep per 20mm deep base if people prefer (and could modify the pack contents accordingly) ?
The Large Cannon & Large Catapult kits, I'd expect would be quite long, and would fit on an 80mm x 20mm base (two 40mmx20mm bases placed end-to-end), sound ok?
The Monstrous Woolly Mammoth would be big enough that a 40mm x 40mm base (two 40x20 bases side-by-side) would be needed to accommodate it.