Pricing for older SN 2001 (or just pre-2001)

I'm looking to get a boat loan for a 1981 Ski Nautique (anniversary edition, very similar to a 2001 model, but the year before).

I need to get pricing on the boat (blue book value in a sense), but when I use NADA I get a price much lower than expected and I fear I won't be able to get the loan I need to purchase the boat. I need at least a 6-7k loan to get the boat (price is a bit over 7), but NADA says somethign like 2k...

Anyone have any tips on how I can approach my lender about this? She wants me to look up the blue book value, and I won't lie about it, but I want to know if anyone has gotten a loan for an older boat like this and had the same issues? I've got a grand to 1.5k I could use cash, so that'd be 20% of the purchase price, but if the NADA value is so low, I don't know if I can get the 6k in loan.

Thanks!