The prices vary according to whether they are 2 digit, 3 digit or 4 digit radars. I've paid up to $75 for a 2 digit radar. To see some high priced ones that are very desirable, this site is one of my favorites: http://coolserialnumbers.com/SuperRadars.aspx
There are one or two listed on that site that I could add to my St. Louis FRN district collection. The price is high but not terribly obscene. Serial Number H 21111112 A 1969D $1 Federal Reserve Note Condition: PMG 65 EPQ Price: $115 Serial Number H 25555552 I 1988A $1 Federal Reserve Note Condition: CU Price: $100
Nice frn! If I hadn't gotten such a good deal on my 03000030 notes, I would have gone with the #1 and #2 radars. $115 is not too bad. I found that most of the slabbed notes are pretty safe for resale as well. On ebay and some of the other sites, they get pretty close or better than that. I missed one for my set because it wasn't available outside of the U.S. and the seller wouldn't change his mind. It wound up going for $125 + shipping.
Sorry for butting in and I know it's not an American note and that the serial number is 'only' 7 digits and not 8 but... This was my very first radar/binary I picked out of a new stack from my bank. Definitely a 'star' in my collection. And, slightly off the thread, my first true binary (as in 1s and 0s only) from circulation.
Nice notes thaivic! No worries about not having US notes, the thread isn't limited to only US. Radars and fancy SNs happen all over the world!