CCR people are very happy to talk about using helium whenever they feel like it. A deepish and long dive would use as much as 60 litres of helium -- call it 10p/12c, then it's a mere £6/$7.20 per dive. Plus another 90 litres of oxygen -- about 1p/1c = £1/$1. Plus the sodalime, about £5/$6. Plus a pee-valve catheter, about £2/$2.
And the boat fee, £60/$70.
And the diesel to drive to the boat.
And lunch. And a nice day out.
All for £100/$120.
Alas the cost of a twinset fill for a 60m/200ft dive would be £££++/$$$+++
The reason I'm going CCR