theres no cheap way of doing it really im afraid mate! you will need to buy as you said a 9141 compliant cable, and you need it with ELM327 compatability if you want to use any diagnostic software.
To remap your ECU you will need a ECU flash unit with EEPROM and then some flashing software which yes there are plenty of freeware versions. To be honest mate id go somewhere and get it mapped professionally if this is all new to you because many 'tuned' maps that you can find on the internet are pretty useless and will decrease your performance or some are even blank maps which obviously dont do a thing and could screw your ECU up for good, other maps are too generic for your car and could damage your engine after a while.
Unless you know how to make your own maps i wouldnt attempt as personally i would never go anywhere near a map id found on the interent or bought from a disk of 10,000 of ebay!