@Peitho I have finally discovered why the runner up prize is a measly £4! 
The value of the Oh! Points was dramatically reduced back in 2015 when they changed how they worked. 2000 points went from being worth £10 to just £4, and the RotM prize was never upped to compensate.
I think this strengthens our case for a prize bump considerably. 
Current Costs:
12 winners @ £100 = £1200
36 runners up @ £4 = £144Total = £1344/yr
Option A: (return to pre-2015 prize value levels)
12 winners @ £100 = £1200
36 runners up @ £10 = £360Total = £1560
And 1560 - 1344 = +£216/yr (+£18/month)
So roughly an additional 16% cost.
I think that seems quite reasonable. (even more so now we know it used to be this )
Option B: (give the prizes a modernising flourish)
12 winners @ £100 = £1200
12 silvers @ £25 = £300
24 bronze @ £10 = £240
Total = £1740 (+£396/yr or +£33/month)
A national campaign for less than £2k annually? That’s a bargain.