Air Conditioning - Outdoor unit will not come on??

We have a very old unit that has been working perfect until late last night.
It seemed like we had a power surge and we heard loud humming from the unit outside. When we attempt to turn the unit on we can hear a double clicking sound coming from the unit outside but it will not cycle on. The clicking sound is the same that it used to do right before it would come on. Anyone have any idea what might the problem? We are assuming we will need to replace the whole unit. Very frustrating when you cant find out how much a new unit will cost. Dont want to have someone come in and charge us double for a new unit. Any web sites that show prices of new units?
We have an in home day care so we will need it fixed or replaces right away.

First check and see that you have 220V power to the unit . Breakers or fuse.
Dont say you need a new unit till a tech has looked at it. Cost cant say cant see the job or know the sizeof unit .So get 3 bids for sure. ;)

We are wondering if it is a power problem. I forgot to mention that early today one outlet in our kitchen has no power to it(last night it was fine). From what I can tell the SAME line that goes to the outlet is the same line that goes to the central air unit. hmmm Not good with electric so I will what for the repair man to show up.

Could be one leg of your 220V line is dead then.