They were expensive indeed. Many "super sports bikes" - as the category was called - from the established brands, like the Gazelle Tour de France and the Batavus Sprint, would retail at around 500 guilders in the late seventies. The Champion Mondial semi-race would set you back all of 1,120 guilders in 1978.
What you got for more than twice the money was a bike weighing 13 kilograms instead of 15. Or so Gazelle said in their 1978 brochure. I guess they were very conservative, as I just weighed my 62cm bike at 12.3 kgs.
Interestingly, the PX 60, which was sold in Holland until 1976 (priced at 995 guilders at the time) was cataloged as weighing 11 kilograms.