Here are some SAG rates:
http://www.entertainmentcareers.net/acting/sag_rates.asp
However, that is for a nameless, one-time character who has a small speaking part.
If you are Norm in Cheers, or even Paul in Cheers, your rate was negotiated by your agent. The more often you appear, the more popular you are in the show, that all determines how much the producers are willing to pay. $10,000 to $20,000 per week would not be out of line for a new, semi-regular character on a hit show. My guess is that later in the series, Norm and Cliff were getting WAY more than that on Cheers.
But there is a fine line…two actors on CSI got fired (and then re-hired when they begged to get their jobs back) after a failed attempt at bluffing for more money.
Sharona (Bitsy Shram) from the show MONK can tell you the perils of thinking you are invaluable to a series and hold out for more money…they canned her ass and found a new actress for the part.
By the way, to get a SAG card, I believe you need to have three spoken lines on a show. I remember sitting with actors watching a television show and when the bellboy brought the food:
“Your dinner, sir.”
My friends would yell, “one line”.
“Yes sir, the steak is rare.”
My friends would count, “second line”.
"Thank you sir. "
And my friends would all yell, “SAG CARD!”
And working as an extra in Hollywood, it was always a really BIG deal when an extra was given speaking lines. I remember a women who was hired as an extra was so thrilled she burst out in tears when at the last minute, they told her she had three lines. She knew she would finally be elegible to get her SAG card.