I have a 14 double corrally motor. I tried to break it in using a laboratory power supply that gives a maximum of 4A. The motor just starts to rotate at 4 Amps @10Volts so you get a rough idea. The motor I have will draw a LOT more than the stock though.
Normal solder has a melting point of about 180 degrees celcius
High temp melting solder goes up to 300 degrees celcius but the solder it self is quite expensive (about £15) and you need a high temp soldering iron which will be at roughly £20.the price to get a electronic speed controller for stock motor is at this price range,a bit cheaper sometimes.
For example the mtroniks eco27 costs £20 only.
Convert the money to your currency to get and idea and if you need more help, we are here!
(for money conversions:
www.xe.com and then click on currency converter)