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The official Steemmonsters site has a market built in. You click your card and there is a sell button at the bottom that you also click. I never sold any yet so I am not sure of the full process but there are thousands of cards for sale and transactions being done daily. One card sold for $3000 just a few days ago. Off course there is risk with every investment and you might end up at a loss but if by some chance you hit one of the higher ranking cards you could be in a few hundred. I guess it depends on if you like gambling or not. I purchased only one booster pack for 2 bucks and hit a card worth over $1000 USD and then there are others that bought hundreds of packs and haven't hit anything as valuable as the one I got.

Here is the steem monsters official site. You can look around without a log in. https://steemmonsters.com/

Edit : you can buy steemmonsters with crypto also. ..... Steem / SBD and others. I am not sure if the kick starter takes crypto or not. I never noticed the option but I wasn't looking for the option either.

The $50 option is all sold out already .. there is a $25 option still in action. It looks like the $25 option has unlimited spots unlike the other options. The next lowest bundle is $200.