You are correct in the general price range assesment you mention
. I have a couple of Japanese works from Ningen Kokuho..... and think ofthem as the "retirement fund"
I have purchased scrolls (I have a small collection) mainly in Japan but also on EBay. As was stated already by Victoria, if you are using EBay...... look at the feedback of the seller very carefully AND read the descriptions even more carefully. Sometimes a little "tiny" lack of information in that description can make the difference between a "good deal" and a "ripoff".
"Authenticity" is always a potential issue when you are not fluent in the language and the stylistic conventions of the genre' or the period. And when you can't examine the piece yourself in person.
Watch out for particularly beautiful looking pieces that are pretty darn cheap........ they often can be screen printed. If the EBay listing does not then also specifically say "hand painted on silk" or something like that....... it probably is a cheap reproduction item.
If you are buying strictly for the "general aesthetic"...... then you have a bit more latitude in your considerations. If you like the scroll in question and feel OK about the price you pay...... then it will make you happy. Nuf said.
I have bought "real gems" in Japan for as little as 500Y (About $5.60 US) at temple fairs and in out of the mainstream little antique shops out in the boonies of Japan. (It helps that I can "chat" a bit with the seller.) But most are more expensive than that. You likely can find some generally nice ones on Ebay for somewhere between $50.00 and $100.00.