So, using a search engine is beneath you? 
Must forum minions fetch the answer for you?
Oh, plenty:
https://hearthstone.wiki.gg/wiki/Solo_Adventures .
I believe all ‘paid’ adventures (and some are free) are purchasable with gold now, so it depends on the definition of ‘paid’.
https://hearthstone.wiki.gg/wiki/Adventure#Patch_changes
Oh, one more small thing: if you don’t see all the free staff in the game, acquire it from the web shop (using the site or client) — it’s free, you just need to click it there, then it should appear in the game.
PS
Oh, yes. Moreover, my recomendation has long been to avoid buying stuff, especially for money, there — it’s more fun that way. [1], [2], [3] By the way, their deals are terrible — you really don’t want to spend your money on them, it’s as if they don’t want you to do so either.
With that said, I’ve blown a lot of gold on Mercs packs, fishing for legendary (mostly) portraits — but hey, that’s been my gold with not much else to spend it on, otherwise it’s probably a terrible idea, especially given how bad those packs are. Unless you really know what you’re doing, I wouldn’t recommend that.