It is a blatant rip off but...
There is free parking both at Glasgow and at EMA for drop offs and pick ups.
There was a woman moaning in the Business Section of the Sunday Times last weekend saying how badly she'd been ripped off at Luton when she'd gone to pick up her son.Luton offers two hours free in the long stay and I think c30 mins in the Mid Term. It's abit inconvenient and you have to use the Shuttle bus, but I'm afraid that's the way things are. The trick really to minimise cost on pick ups is to drive around and find where the taxi drivers are parked waiting for their clients to phone them and park there and await the call.
Incidentally I'm just an ordinary punter.