The reason I as seeing if there was a cheap fix was due to the amount I have in the bike already.
Sure I want to do the job correctly but I just can't spend an arm & a leg doing it if I'm going to get my money back when I sell the bike on. Searching for a new arm now, may have to consider switching both of them so they match. Not what I was hoping for.
Aluminum foil or locktite may work, there is certainly nothing to lose from giving them a try. The best cheap fix that is certain to work, is to buy a left crank arm that doesn't match the crankset and ride your bike. Then you start looking around for a matching replacement at a reasonable price.