Thats what Im getting at,
How much power do you want ?
If you don't go chasing 200hp or 9000rpm then you can eliminate £1000 worth of pistons and rods, and the associated engine build costs.
If you limit yourself to head work, cams and intake mods, this can be done with a "Track & Road" remap by Steve G.
It can even be done on another head, so you could put it back to standard for resale, and swap the modded head and intake on to your new car.
Stuarts (PP) Kits are very good, with a lot of work behind them and a warranty.
But they don't suit all Budgets. There are many other people tuning Sigma engines, (Shawspeed, BPJ - Big Paul Jackson) who have not specifically targeted caterham owners.