Mate, good luck, I have been thinking about the same thing for a while now but the problem is that prices for NRL cards are subjective, I mean they are only worth what someone is willing to pay for them but I agree with the school of thought that as your collection grows that has to be an increase in value as it becomes more complete.
What I am going to do is this, start with my 1988 base set and research a replacement value, do that for all the base sets / albums then factor in the inserts / auto's etc. You have to be realistic with the value to replace by that I mean you might pay 200 dollars for a 1996 all fired up Brad Fittler auto (3 card set) but another could go for 80 dollars, in that case I will pick a figure around the middle of say 120 - 130 dollars and will give that to all the '95 and '96 auto's.
have to agree with dave. unfortunately something like that pretty much have to do the foot work yourself. the only thing i could suggest is that there a lot of very knowledgable people on this site who really know there things when it comes to cards. so they may be your best bet. but once again it comes down to what they would be willing to pay
If you are happy to go through your house insurance, try contacting your insurer and see if they want all the details. With mine i just added a sports card collection as a specific item as part of the contents insurance. I just said i wanted $x of coverage and they said it would be $X more on the yearly payment. Might be worth a try before you go to the effort / expense of a full valuation.