As the price of rares is really dependent on your particular server, it's kind if hard to give an accurate average.
On Butcherblock, a Severed Alder tends to average about 10g (outrageous), but they are bought up very fast. T1 rares are very rare, as OBD states, because most people are only harvesting T1 nodes for a very short time. You will find an occasional one on the broker, but you really have to be quick to buy it. There are many Market Sellers who will snatch any rare they can find at a cheap pirce, then mark it up themselves for sale.
May I inquire as to why you are asking for a price average? There are many people here who could give great advice based on that answer.