No, there is not. He might want to stick to "casual mode", but the difference with ranked is thin at best.

I don't think Arena is a great solution either. Sure, it levels the card pool for everyone, but without some experience of the game a new player will mostly get wrecked. In that case it will just lose him gold.

Now legendaries are not necessarly the big issue (although Dr Boom is laughing at me right now), but the card pool more broadly.

Example : wanna play Druid. Wait, you have no Ancient of Lore (epic), no Wrath (common), no Starfall (rare), no Force of Nature (Epic), no Druid of the Claw (common), no Keeper of the Grove (Rare), no Ancient of War (Epic), and that's just for the class cards. Without any of those, your deck will just be subpar at best.

Sure commons are cheap, but when you're fresh to the game you have none. 40 dust each tends to add up quickly when you need alot. Craft 10 commons (and boy do you need those Druid of the Claws) and that's 4 rares you haven't crafted in terms of dust. It matters.

Then there is Naxxramas, which contains important cards (Loatheb and Sludge Belcher most notably). At it isn't cheap in terms of gold.

My best advice would be to look for decks tagged as "budget" on dedicated Hearthstone websites. Aggro decks are probably what your friend should look at first, as they are usually pretty cheap and they'll always win some games every now and then. What's more, games go quicker with them, and that matters a lot when you're new in my opinion.

Also look for guides and videos from good players. Trump, for example, usually explains what he's doing and does it well. He also has a serie (Trump Teaches) designed to help people new to Hearthstone and TCG/CCGs in general to get the key concepts. He plays both Constructed and Arena (tagged as "Trump Cards"), and posts videos very regularly.

But anyhow they'll be some grinding and some struggling, be sure to support your friend !