splicing together 2 peices of 4gauge wire?

ok this is the LAST step in my wire hiding advendture. i need to extend the starter cable. i cannot afford any mor 4 gauge cable. i have the full lenth stcok one (with the ring terminal for the starter solenoid cut off) and a rockfor fosgate amp ground wire ( 4 gauge) that is on the starter solnois and is 5 ft long. i spliced the and taped them just to get the car started but i DO NOT feel safe with it setup like that. how would you splice them together? would you keep it like i have? solder it? how )torch and solder, soldering iron etc...)? i was also thinking of attaching 2 ring terminals to the wire ends and sinpmly bolting them together and shrink wrapping taping and wire looming them for protection. wat would you do? thanks alot! and remeber, all new wire is prett much out of the question.
 
Solder would be the best way....however. Seriously, 4 gauge wire and two eyelets can be purchaced at any auto parts store for like $5.