USAF .22 Conversion Price

I was wondering if anyone here knows what a USAF .22 conversion is worth. From what I was able to dig up on TOS, it looks as if they are more desireable than the M261 conversions, but I couldn't find any info as to what a used on would go for. I'm looking into selling mine (I have two of them with 6 mags - 3 of which were NIW when I bought them 6 or seven years ago). I'm looking to get a dedicated upper, but need to sell these conversions to help fund the upper. Thanks in advance!