My SO's chevy trucks power steering cooler up by the radiator sprung a leak.
Right now its bypassed - just hooked the two hoses together eliminating the small radiator
The existing rediator consists of a small pipe that runs up and back down covered in fins ( next to engine cooolant radiator- not part of it )

question is....what do you guys think about me taking a 6' length of copper pipe and making a coil of sorts to replace the leaking cooler ?

I found this for around $20 but the copper tube would be an easier fix I think
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Power-Steering-Oil-Cooler-Imperial_19230069-P_N3200D_A%7CGRP2070_____

Most cars/trucks didn't use to have a power steering fluid cooler.  The first (early) power steering cooling set up I ever noticed was the 3rd generation Camaro's (at least the Z28's) had metal tube that ran from the driver's side to the passenger side under the radiator and after making a 180 degree turn ran back to the driver's side where it connected to the hose.  This circulates the power steering fluid through a thin metal tube in a high air flow area.  It can only  be for cooling the fluid.

You could increase the surface area by coiling/looping the tube to make it longer from entry to exit of the fluid.

either leave it bypassed, or get a small trans cooler

Its not really all that necessary for the truck to run just fine.  But I would recommend doing the job right and either have a hose made at a local shop that bypasses the cooler (not a splice or quick fix) or replace the cooler.  Several auto parts shops have a trans or universal cooler that should do the trick.  Just make sure its rated for petroleum products like trans fluid.

But since it will be almost as much to have a hose made, why not just replace the cooler?

I have the 7' copper pipe in the workshop $0.00 and brackets to hold in place $0.00
Copper+power steering fluid?  shold be fine right?

If I dont have to spend the $20 on the universal kit which will end up being just as difficult to install why not use parts on hand.?

If the copper line is rated for the pressure it should work.  Some "coolers" are just exposed metal line close to an area with high air flow.