Nothing really, seems it cost about the same as it did a while back.
I googled for an old Argos catalogue - here's one from 1990:
Argos catalogue from 1990 filled with lots of retro goodies. From Retromash.com
issuu.com
Here are the sets they sold back then:
Now it looks like the "Pole Position" set in that old catalog is the closest match to the "Grand Prix Racing Set" they currently sell - both come with two F1 cars and a figure of 8 track, the new one is a slightly smaller tract at like 17.5 ft rather than 20ft but comes with crash barriers and what look like better cars, the old set has some smoke feature though.
Now accounting for inflation £62 in 1990 is just under £150 today... and that set on the Argos website is selling for £160 so, basically still costs about the same as it did when elder millennials were little kids.