Chump change in the scheme of things. Besides a jail term of up to five years, the potential fines for flying a drone within a UK airport's NFZ are unlimited, plus you would almost certainly be taken to civil court for damages by the airport concerned. After the Gatwick fiasco anyone considering this can expect more technical countermeasures to be deployed, an immediate increase in police presence following the first flight, and a police force / Crown Prosecution Service just *itching* to throw the book at someone. We're definitely not talking the typical slap on the wrist for chaining yourself to building here; getting caught doing this could ruin your life.
Like many strikes and protests they'll also find out the hard way that annoying Joe Public as well as those in power you are trying to disrupt is the surest way to make Joe Public lose any sympathy for your cause. Remember all the comments from irate Gatwick travellers who would quite happily have lynched the perps last year? Yeah, that's *just* the reaction you want from people that you are hoping to act more responsibly towards the climate, isn't it?
Unless it's a false flag operation, then "dumb" doesn't even begin to cover how ill thought out this plan is.