I'm in a gambling mood but I've already used my 250 vending machine pulls. I don't want to do slots, scratchcards, or loteery. Are there any items you can open to try and get rare prizes? if so what are the possible rare items.

HERE is a list of all the chance items you can get in various places on subeta. Read the item notes to find out how to obtain them

You could also try the coin machine. Here's a thread that someone did recently where they gambled a lot of coins. The results were... actually not as bad as expected.

Gambling away - 12M in Special Coins

You could also try the Mystery Box. Every day, it pulls items from a random shop with the opportunity to pull some retired items. Today is the Food Market!

Is there a limit to how many times a day we can do that? This one is fun too! I haven't gotten anything worth more than 20,000 sP so far though.:p

It's really hard to get a super rare item from the mystery box, and usually only those are worth over 20k. If it was the book shop, it would be a different story, but if you're looking to make sP the mystery box isn't a good way to do it.

I'm not really sure - as far as I know, there isn't a limit. As said, the Mystery Box isn't the best way to make profit. The draw of that is getting the achievement and the possibility of getting retired/rare items.