It depends on what the condition of these rifles were in and what might have come with them. It seems that for a NIB-99.99% condition rifle are now in this range. Of the three 90 series Hk rifles though, the Hk91 is the most abundant of the rifles as they had the most brought in the country at the time. If the 91's you saw were in the NIB-99.99% condition and you put your money on them, you would not be loosing money. They only increase in value as time goes along. I'd bet in 10 years it won't be unseen to see these go for $5k (at the NIB-99.99%). If you have the money to spare, I'd go get one of them if they are in that condition.
I personally like the 93's. At the time, I paid way too much for mine, but now I'm glad I did. They have gone up significantly in value since I "paid too much".