MTG

I think the absolute cheapest would have to be pauper, and depending on what your flg nearby runs you may be able to find games to play with others without too much work.

As the name suggests, Pauper is the go-to budget format. Admittedly, it's less cheap than it used to be. But at its cheapest, it is one of the least expensive.

EDH (Commander) has a huge range in price, but some decks (check out The Commander's Quarters on YT) are super fun and affordable. It's a good casual format to start a budget deck with and continue growing. It's also a gateway drug, so be warned 😬

Lastly, if you are playing in a private pod (i.e., not at your LGS), you can set your own limits based on market price. For example, no decks over 50 bucks total, no single high-cost card over 10 bucks, etc. Ultimately, rule zero applies to budget-conscious private games. You decide what's allowed.

Thanks all for the answers, much appreciated

I don't know if it's the cheapest but I recently got back into magic after 15 years and my friends have been playing eternal brawl.

It plays really well with 3-4 players but works for 2-6. Like commander you have a commander but only 60 cards and all of your cards need to be from a block to avoid bad combos.

It's possible to set up a deck for a few dollars if everyone is avoiding expensive cards and using a few sets old block usually means most cards are a few cents.

https://eternalbrawl.wordpress.com/formats/

+1 on Pauper! Just created a new community here for it as well:

https://mtgzone.com/c/pauper

I agree with others that pauper is a great format to get into as it can be very price assessable.

However I would like to make an alternative suggestion - JumpStart (or a mini JumpStart Cube if your group is very interested). The biggest benefit to this format is the sheer variety that you can have in games over the course of an evening of playing. It is very easy to pick up and play from a players perspective and can be treated like a board game. It will require someone doing a small bit of research on what packs you need to buy, or what singles you need if building a custom list.