Depending on how the art is, you could send them to a screen printing or risograph place.
Make the sleeves yourself, buy some thick paper, like 300-350g with a nice finish and have the artwork printed on it, then fold and glue it yourself.. Its alot of work but its definitely the cheapest option.. Get a professional to do the printing though, its not as expensive as you'd think and its totally worth it, if the artwork you got it any good that is..