Another way of seeing it is to have each element have some thing it "wants" and have the druid either perform that as a quick "ritual" unless they choose to avoid it. Like, if you want fire to do something for you, you need to give fire what it wants which might be e.g. more fuel. This might be weird in fast-paced combat situations, but otherwise maybe you need to sacrifice a bush or a tree or something, and only then will the fire spirits do your bidding (e.g. forge a sword for you, or burn someone's house down).
If you really want to you could make it a debt thing; you can have the druid be the guy who always says "c'mon spirits, I'll make it up to you later!" Then during downtime, he'll actually have to let fire loose on a tree, or bury a few coins in the ground, or make a burnt food offering where the smoke reaches the air spirits, or spend the whole night meditating by the forest pond, or whatever. Ideally you'd do this without having to keep a tally of "favours owed" for each element; if the druid in question said "yeah, that's the way it works" I would pretty much limit them to one unpaid debt per element at a time. Effectively, if they owe the fire spirits something, they must choose "you avoid paying nature's price" if they ask fire for another favour before paying back.
That's a specific type of druid though, and it might be harder to mix and match with other types of "nature's price".
For more general ideas, make the elemental spirits have personalities. If the druid asks the earth spirits to block the door, tell them this particular mountain is very greedy and requires them to sacrifice some gold. If the druid asks the wind spirits to ease their fall, tell them these wind spirits are very vain and will tear away their fine clothes. If they ask the water spirits to bring up water for them to drink while they're trapped in the cave-in, tell them the waters of this area abhors fire, so they need to put out all torches before the water will comply. In general, give the spirits something concrete they want, that doesn't have to fit into what all water always wants - it's what this particular water spirit wants.
A general problem with the option of "paying a price", I think, is that it sort of has to be something physical and concrete in order to work in an immediate "I do it in order to cast" sense. If the price is that you return an stolen artifact, that's cool and all, but you end up a) creating a future obligation that you'll have to remember, and b) introduce the option of not making good on the deal later. Of course, if the druid starts ignoring their obligations the spirits might come for revenge later on, but that's still a "note down for the future" which is a whole other flavour of the move. If you like it, it's cool though.