Something to consider is that in two or three years time it's quite possible that Heljan's standard releases of these models (assuming they do incorporate them into their standard range) could easily be around the £100 mark, even when discounted. Just look where the prices of Hornby (in particular) and Bachmann have gone this year. With high inflation not looking likely to end quickly and, perhaps more significantly, ever rising costs in China, three years time seems very likely to bring much higher prices.
However, Heljan are unlikely to release them only as twin packs so there will still be savings to be made if only by obtaining only those locos you actually want.