You can estimate based on the data sheets.
An example:
2-1/2 Ton 208/230 Volt 1-Phase Scroll Compressor Direct Factory Replacement Part (Copeland): American HVAC Parts
is a 2.5 ton compressor at 2.5 HP
You can assume a 1/3 HP outside blower and a 1/2 HP inside blower.
2.5 + 1/3 + 1/2 =3.33 HP
Add about 25 W for controls
Running watts would be about 746*3.33 + 25 that 2486.8 W
Call it 2.5KW; there are 746 W/HP
At $0.15/KWH it's about 2.5 KW * $0.15/KWH = $0.375/hr to operate
If it runs 5 hours per day 5 * 0.375 * 30 = $31.75/month
Hopefully, my math is right. Running time could be off. Each month could be different because it depends on the cooling degree-days
Once you find a fudge-factor for degree-days, you might be able to get a seasonal cost.
USATODAY.com
Look at the nameplate for similar information.