Normal tattoo parolors charge around $100/hour. A sleeve (depending on the size of your arm, of course) will take roughly 20-25 hours. Thus equalling around $2000/arm.
People normally misconstrue the truth. It all depends if you want a good job, or a half-assed job. Even for a half-assed job, it is very doubtful to get anything under $2000. My two sleeves cost me $5500. I am a bigger guy, 6'8 with 22" arms. More ink, more space to cover, more cost.