I guess it depends entirely on your definition of expensive. The drains themselves, you do not want to cheap out on. Good quality drains will likely cost you $50 or more, each. All this is required to remove the existing drains is to clear out the cabinet under the sink and look in there. You will see a the drain coming down from the sink. There will be a threaded piece with a large nut screwed on to it. That nut is holding the bottom piece of the drain to the top piece of the drain. Unscrew that (it probably won't be easy if it's been there for 50 years). Then you can lift the top part of the drain from the sink.

Re-install in reverse order, using plumbers putty to seal between the top drain piece and the sink. Generally, I've found when replacing sink drains, that some or all of the drain pipe will need to be replaced as well, so possibly another $20 or so in parts. Those compression fittings like to leak once they are disturbed. Although I am capable of doing it, I HATE messing with drain pipe and prefer to call a plumber to do the job. A plumber will do the job quickly and easily.

Thank you so much....I will be calling a plumber this week...
I appreciate your time to answer!