if you can't find a secondhand one Andrews communications have them for abot $90 for a correct image its a bargain
Another good one but more expensive is the Stela Vue one with a focusable correct image diagonal excellent quality . you can use is as a small telescope i've used mine with a 4.8mm ( about 20 X ) Nagler and gives excellent images some people even use them for photography ....about $130 USD still a great deal though
Zane