The formula for least-expensive game per hour played is simple: Multiply the house advantage by the number of plays per hour, and multiply that by the minimum bet size available.
Odds bets in craps have a low house advantage, but you play many times per hour. And usually the minimum bets are not that low.
Blackjack has relatively few plays, a low house advantage if you play basic strategy well, and you can find low-limit tables.
For example, let’s say you play 60 hands of blackjack per hour, without card counting but playing solid basic strategy. You’re playing a six-deck shoe game, so the house advantage is maybe .7%. You can still find $2 minimum blackjack tables. So, you will be bet a total of $120/hr, and the house will take .7% of that, so your cost per hour is 84 cents. That’s very cheap entertainment. Of course, there’s also risk involved, so expect to lose or win in an amount 10-20 times as great. Craps plays about twice as fast, and usually the minimums are $5, so even with roughly the same odds the game will cost you more than 4 times as much per hour to play.
You can play a game like Roulette, which has a house advantage of 5.26% - almost 10 times as large as blackjack. But in roulette you might be able to bet as little as 50 cents per spin at some tables, and you only get about 45-50 spins per hour, so even that game is relatively cheap. You’d be betting $25/hr, and the house would keep a little over 5% of that, or $1.25.
The difference is that playing roulette in such a way makes it very hard to win, because the house bias is so strong. In blackjack, the house edge is so small that over a short session of an hour or two you’re close to 50/50 in terms of your chance of coming out ahead.
What you really, really want to avoid are the sucker bets. Don’t bet the hardways in craps. If you’re going to play blackjack, learn basic strategy. Stay away from the proposition games like the big six wheel or the various money wheels. Never sit down at a game where you only have a vague understanding of the strategy.
If you want to play for enjoyment, just remember to bet small, bet slowly, and bet smart. You can play a little craps (pass line bets, take the odds), play a little blackjack (if you don’t know basic strategy, ask for a lookup card - a lot of casinos will let you have one). Hell, you can even put a few small bets on roulette. The objective is to have a good time and not lose your shirt - not necessarily to find the absolute best odds in the house.
Get up and walk around, try out a handful of spins at roulette. Wander over to the craps table and watch them play for a bit, then play for 10 minutes using minimum bets. Then leave, wander around some more, watch a little of the action at the high limit tables, then go play a little low-limit blackjack. Etc. The object is to play very few actual hands or spins or passes, while still enjoying yourself.