I agree with your comment about price and because we are doing engineering work like sandcast patterns and moulds, we use a lot of resin each print, so the cost is significant.
However there is also quality. If you look at the photos below of moulds made for wax , then the Formlabs grey prototype resin is very stable (and is dimensionally excellent), but the Photocentric Firm resin is falling apart after only 3 waxes cast.
We have used the Formlabs grey for sandcasting patterns and core boxes. If you have ever been to a ferrous sand casting foundry, you will know they are not the most delicate and careful workers and yet the Formlabs resin survives the rough treatment very well.
The Photocentric resin has got a ways to go in terms of durability imho.
The Photocentric mould after three uses (printed using FL Grey settings, post-cured 3 hours / 30W 405nm UV.
The FL Grey mould after ten uses - still showing no signs of fatigue.