Hi there! As far as 3DSs go, I'd recommend one of the new models, whether it be the new 3DS or new 2DS. The new 2DS actually feels really nice and includes the clamshell design that wasn't present in the original 2DS. The new models also feature built in amiibo support so you don't have to buy the separate accessory. You can grab a fairly new one off of eBay for around anywhere from $140-$190. If those are outside of your price range, a normal 2DS (no clamshell) might be the move. Those are a bit cheaper than the newer models, and I've seen them run for $90 pre-owned on GameStop, but they are frequently out of stock. I'd first recommend looking around for local listings on sites/apps like Facebook Marketplace, OfferUp, Craigslist, etc., you can find some really good deals there sometimes.
As far as New Leaf goes, most retailers should have the game in stock for $20 since it's now part of the Nintendo Selects series. Alternatively, Amazon offers
digital codes as well. I'm pretty sure the game is also $20 directly from the eShop too.
Hope this helps. Good luck!