Air Conditioning - Running An A/C: Cost Calculation Quest. ?

Hello:

Have moved into a 30 yr old house that has central air conditioning.
Condenser is outside, and evaporator is part of the gas, forced hot air furnace.

Very curious about what it might cost to run the A/C.

Realize there are a zillion caveats involved, but would like to come up with a
very approximate number. Data from previous owner is unavailable.

Tried looking up A/C Cost Calculators on the web, but couldn't find anything appropriate. All seemed to want to know house insullation characteristics, etc.

So:

The unit is a 3 Ton
Installed in early 1984 (assume SEER of 9. Is this reasonable ?)
Cost of electric is 12 cents per KW Hr.

If the unit is running continuously, what would the cost be per hour ?

Questions, and thoughts:

a. is it simply a matter of converting 3 tons to BTU/HR (=36,000 BTU/HR), and converting this to KW HR (not sure how to) ?

b. Does the SEER rating, house characteristics, etc. come into play at all, if one assumes continuous operation ?

Seems to me, and I really don't know for sure, that the Tons of A/C being put out, and the electrical rate are really all one needs ? Is this so ?

Thanks,
Bob

All i have is some old paper work if it helps. This is from FPL the power co. down here

2 ton 9 seer 6 hr run $19.00 12hr run $38.00

4ton 9 seer 6 hr run $38.oo 12 hr run $76.00

cost based on $.08 per hwh

ED ;)