For Sat Diving, you get a Day rate, for each day you are onboard the boat/barge, and a sat bonus, which is an hourly rate paid while you are in the chamber under pressure, seal to seal.
That's the easy bit. As to what that actual rate is depends on where you work, who you are and who you work for. For example, I know of guys working on an Indian boat in Iranian waters for $300 a day, and $12 sat bonus which works out at $588 a day. This rate would change depending on who you are, and what deal you can strike, and will be different to divers working on a boat a couple of miles away, as there is no set rate for the region. Compare that with the North Sea, where the rates are set by agreement between the union and diving contractors, and is currently around £580 a day and £37 per hour (around £1500 a day in Sat, or $1930 in dollars). These are the two extremes obviously, but the industry just now is a buyers market, way too many sat divers around for next to no work, so globally, the rates are nearer the bottom than the top.
As for how long you can work per year, this also varies. In the U.K. and many other regions, there is a maximum sat exposure of 28 days per trip (in Norway, this lessens to 21 days total onboard the boat, so you have to join, blow down, dive for a couple of weeks, deco get on the surface, and clear bendwatch all in 21 days) although this is a hard and fast rule in the U.K., in other regions, its more like a guideline, and I know guys who do 40,50..60 days in one Sat. but this is usually somewhere with lower rates, and guys dig out to make a decent pay check for when they get home...
Then, when you're home, companies have rules and guidelines about how long you have to take between Sats, some have a half time rule (where if you do, say, 20 days in Sat, you have to be on surface for a minimum of 10 days before you can be re-committed.) some have equal time rules...and some don't give a **** (again, some guys will join a boat, do a month in Sat, come out for maybe a week, then do another month before going home again)...and it's not been totally unheard of for a Diver to have two logbooks, and rotate between the two with different companies doing a month, then a month....then another...! This usually happens if there's a fine to pay, or there's been a bad few nights at the poker table...
Oh, and overwhelmingly, divers are self employed, and have no real guarantee of getting called back for another trip, or indeed if the company has any more work. Then there's the companies that pay next to nothing to begin with, then compound the offence by not paying and going bust- so there's no real way of calculating an exact wage (especially if you add in the Tax that you might or might not have to pay).
Having said all that, if you are a fairly experienced, well thought of Diver who tries moderately hard to chase the work, then it's fairly normal to make around maybe £80-100k before tax, but even then, I know personally that it's possible to make £200k+ a year in the good times...