I want to make a 2-part mould roughly covering 3.5sqmtrs but the overall cost is quite large.

Would it be possible to use a cheaper alternative to the Uni-mould Tooling resin (which appears to be the most expensive part) such as a cheap Polyester resin to bond all the layers of chopped strand mat? Or is there another cheaper alternative to the uni-mould system that would give adequate results?

I don't intend on pulling hundreds of releases, at most I would say 5 in total?

Unsure, may do a fibreglass one first and a carbon one later on.

However, the polyester would only be used to bond the CSM to the back of the tooling gelcoat? The part would release from the same gelcoat whether I used polyester or the uni-mould system?