Does signing on the wrong spot void a contract?

I own a club in philadelphia and I had some construction work done to my place. Just some simple paint work and mirror installs. The contractor gave me an estimate of $2500 with a 50% deposit requierment. So far I only paid him $1250 and all that he did was the paint work. I decided to not continue with the mirror installations because it was simple enough for me to do, but the contract stated that he gets $2500 for the whole job. I feel as though he gets half the pay for half the job done. HERE IS THE CATCH- the contractor signed where the "customer signature" was at by accident and i signed where he was supposed to. Does this mean that the contract can be dismissed in the courts because of his mistake???? CAN I WIN the law suit???

I would not rely on the fact that the signatures are on the wrong lines. Both of you did sign the contract and you paid him $2500 which is proof that a contact (that you thought was binding) did exist.

If you agreed to hire and pay him for a certain job and you then breach the agreement he can sue you in a court of law for breach of contract. Do you know if he has bought the supplies to install the mirrors yet? If he has you would be at least required to pay for those and at most the amount stated on the contract.

Your chances are slim to none of winning.
If the contractor had decided to quit half way through the job and take YOUR money and run, I'm sure you would have a fit.
You agreed to a specific monetary amount for a specific job to be done. You are obligated to the monetary part whether you have him complete the work or do it yourself.
Contracts are mis-signed all the time but the leagality is they are signed.
Take the day off and let the contractor finish the job. You'll both be happier and I'm sure it will cost you less in the long run.

Lets say that I will lose...How much will it cost the contractor to get me to that point as far as lawyer fees on his end? Also, will I lose more then what I owe him?? Simply put, how much will this whole dilemma cost me??

Thank you for helping....I greatly appreciate it....

First of all, Lawyers are not allowed to represent anyone in Small Claims Court. This is something you will have to do yourself.(Judge Judy,Peoples Court,Jerry Springer lol)
I don't know what State your in or what the fees to file are there but this would normally fall into the Small Claims Court amount(check with them locally for your limitations) and it is possible to have all of the papers and the service of them done for $69 through some companies on the internet. Less if you do it yourself.
Not a major expense for the contractor to recoup his loss. And he may come up with additional expenses that he may be able to recoup also.
Unless you have a ligitimate reason for not wanting this contractor to complete the job, otherthan, you can do it cheaper, I would bite the bullet and find the funds to let him finish and move on.
If you honestly have a reason for not letting the contractor complete the work, inform the contractor of your concerns and try to resolve the issue before ending up in court.
All states desire you allow the contractor to make an honest attempt to correct any problems unless there is some concern for safety,health,welfare or incompetence.
Any time you have to take time away from your normal routine to go to court to settle these minor issues it will always cost both parties. One way or the other.