When I was hugely into Hearthstone, I believe this debate came up as well when a streamer I watched tried to do F2P runs. In HS, I believe F2P runs are best done with a fresh account (even then, you can still earn your way to a meta deck by going infinite in Arena if you're good at it), but in GU, I don't think that's quite feasible given how long it can take to grind to something that isn't boring. IMO, I'd think the value of 1-2 weeks of grinding ($GODS + weekend packs) which should come to about 50 - 100 bucks should be a good ballpark for the maximum an "F2P deck" should cost.