im just getting an idea as to what people are wanting for a later model GS tank and seat.  not ready to buy yet unless its pretty cheap. either as a pair or just one, whats the going rate?

There are lots of new tanks on ebay. The later model tanks go from under $100 (may have a minor scratch or couple paint chips) to over $400 for a brand new one. Lots of choices for colors so you should be able to find one that matches your bike. If you don't find what you want, just watch ebay as the tanks available change often. Use this search string:

gs50* tank

Check to see if the tank comes with cap and petcock. If you're replacing a tank you can take those from your old tank.
The older style tanks are virtually non existant. I did find 2 brand new ones for $400 each. Haven't seen any other ones in the past couple weeks.

Seats are easy to find. Condition varies, but usually $50-$75 for one in excellent condition.

You can sort your search by distance from you. You might find one local and pick it up to save on shipping (but might have to pay sales tax if from a dealer).

Hope this helps.