My sub got hit in a lightning storm and no longer works, the fuse is good I think the amp is bad, can I get a replacement amp or is it cheaper to buy a new sub

More than likely the module/chip got fried by a voltage/lightning spike.
It's cheaper to replace small appliances than to repair them.
Suggest buy a new one.

kicker l7 is goog i mean good.lol. any way logic sucks buy a kicker amp or a hifonics amp its cheaper and works just as good. vminnovation.com has them at unbeatable prices. i think the bxi 1210d will work perfect for an l7

It is most likely the power supply burnt out. The capacitor's inside are made cheaper than the o'l days and get overheated easily. You can test capacitors with capacitor tester and service manual. You can test power supply output voltage with just a voltmeter

check that the ground wire is bolted tightly to the chassis of the vehicle.

Although lightning damage is normally fatal to anything with electronics inside, you might remove the back panel and look for fuse holders. If you find one (minimum) or two (likely), replace them (if you have a cheap multimeter you can check for continuity) and see  if it will turn on. You may have to do a little telephone work to locate the high current fuse which is probably 30 amps.  
If you live in an area of frequent lightning strikes, investing in a 'whole house' surge arrester makes sense. These are installed in the main breaker box and any brand I've seen comes with a $10-25,000 insurance policy to replace any dead appliances that fail despite the surge protector. They cost $150-250 US plus installation which you can save if you are afraid to DIY.     

I had the same problem. When I opened it up, the fuse was blown, and it was a pain to find the fuse it needs (3 Amp, 250 V slow-blow fuse, 5x20 mm). Also, the 2 large electrolytics (big purple things near the amp) and one small capacitor were all blown. For 4 fuses, bought seperately from, and the 2 electrolytics and 1 capacitor, it cost about $20, plus almost 20 more in shipping, which still isnt bad considering the original price of the sub. However, the tricky part is that you have to know how to use a soldering iron to take out the old components and put in the new ones.

Had one doing similar recently, and after a thunder & lightning storm. Nothing worked, but kept blowing 2 amp fuse in thermostat, when anything tried, heat or cool. Pulled plastic control box down from inside upper unit (AC) made sure breaker was off, took of plastic cover and smelled inside, and could smell burnt plastic smell. Replaced, control box, that got fan only working. Tried another thermostat , everything worked as it should. Turns out the lightning, or power surge, or whatever, shorted out the thermostat, and control box at same time.

I don't know but seems to me that electrical storm did not cause this, a car is a pretty protected environment (also for the electrical equipment) for such stuff, unless you had a direct lightning hit.
I presume that a hit will be very noticable and I always heard that cars are very seldom struck and therefor are a very save place in that respect.
If it is caused by the electrical storm , I would try to disconnect the battery for a period of time and try again before replacing computer and such.(check fuses to rule everything out)

If the voice coil is blown the cheaper and the only thing to do is too replace the sub. And if it was a new sub see if under warranty and see if they replace the sub
Probably audible distortion make them blow.
Check the crossover for correct settings. Also if you have them in the wrong size box

Check this out: http://www.techlore.com/article/14696/