mercruiser 140

[Fr. Frank]

That will work, but be aware that in will greatly increase gear wear, as you WILL grind the gears every time you shift, AND, if the problem is in fact the shift cable, you run a very real chance of inadvertantly bypassing neutral and shifting directly from Fwd to Rev or vice versa, which has a nasty tendency to blow up your lower unit and/or crack your U-joint.
My sincere advice is to pay the money and replace the cables (plural). You can undoubtedly find a lower price. I asked my mechanic, and he said it should take 5-6 hours plus parts to replace both cables and interupter switch. This assumes that every thing else is in good shape.
Check around for prices on getting this work done.
PS, it's simple enough to do yourself if you have a Clymer Mercruiser manual.