When I was looking for my dovii I would have been willing to pay $45 for a dovii that size in good condition. They are not very common in this area though. I ended up having mine shipped to me so with shipping I would have paid almost that much for 2" - 3" dovii had I not ordered some other fish at the same time.
I paid 30.00 for my male which was 6-7 inchs...my females I got from the LFS, they were marked as Jags in the tank....I paid 3.00 each for the girls...
$45 isn't too bad depending on how it looks but $20 sounds like a good deal. My lfs had a beautiful 12" trade in for $49.99 and I thought that was a steal.