First of all, going for a cheap sub is a waste of money. If you don't want to sound like a ricer, spend a little more and get something nice or go with your current setup.
Secondly, if your speakers just aren't getting any other problems then it isn't because they are blown. If your speakers are blown, you will know. They will get just as much power but will be distorted sounding like crazy. How do you know if it was a power surge? First and foremost to a thinking "no power + power surge" is blown fuse. Check your fuses. Does your deck still work? Is it aftermarket? That could be a fuse blown. What kind of car do you have? It could either have a factory amplifier for your speakers or maybe you have one installed, cause a connection from that could have loosened or something.
Anyway, chances are if you had a power surge you just blew a fuse. That is the only real explanation for both speakers to have no power, because as I said if they were blown they would still be getting power.
