luvdoggiez,
Well Sir, as has been stated, you didn't mention your chassis manufacturer. If, it's a Freightliner, then that tank will run you about $130.00, plus or minus. It is a specific size, shape and design. It has multiple outlets etc. for various hoses etc. You just don't go down to Auto Zone and pick up a $19.95 replacement. Ain't happening.
Many threads on this and IRV.2 about that surge/overflow tank replacement and, how to protect it from future element damage. Many guys simply get some aluminized tape, (the kind they use for A/C ducting) and tape it all up to reflect the elements.
But, not only is the cost a factor, but replacing it, for many of us, is shear terror. They didn't give much room for most fat fingers and wrenches in there. At least on mine and several friends who also have Freightliner chassis.
And, as for picking one up from a junk yard, well, yeah you can do that but, how long has it been in service? How long has it been sitting in the elements? You're better off biting the bullet and getting a new one and be done with it for years. UP to you. Good luck on the change out.
Scott