I'm sure David can supply both quotes.
Reconing can definitely change the power handling depending on the parts chosen.
If you find a different motor to have it rebuilt, then the only original part is the basket.
After looking at the MX line of subs, why do you want to change the motor? Since that sub doesn't use any standard parts, finding a different motor will be difficult if not impossible.
the sub I have is in perfect working condition now
Then why the recone?
The re mx have the Neo magnets would it be possible to get a more heavy duty bigger magnet on there
If you can find one that fits, you can probably get a bigger magnet but not one more powerful. Neodymium magnets are known for their strength. Just because a magnet is big doesn't mean it is more powerful. You have to look at the material and motor design.