Can anyone tell me to find out a price ?  

I have checked a number of second-hand motorcycle sales sites and none of them seem to mention Bridgestone or Rockford. The Bridgestone factory actually stopped production in 1969 and was taken over by Rockford according to one site. I can find pics there of a 1971 Bridgestone 350 GTO (but, frustratingly, no prices). I can only assume that Rockford continued production of some Bridgestone models and continued to badge them as Bridgestone.

eBay (UK) has nothing (only Bridgestone tyres which, I think, is a different company); Autotrader and Autobike (both working sites) list neither Bridgestone or Rockford as a manufacturer. There are a number of other promising links I found which are closed or non functional.

I am not a dealer or specialist in bikes but I do have dealings in antiques and books. In cases like this, where there seem to be no records of sales, the only thing you have to go on is the prices of similar bikes. Since there doesn't seem to even be a Bridgestone 'fan' site, I can only assume that the bikes were less than spectacular and, very likely, much of the bike was bought in rather than factory designed and produced. I could be wrong but a small factory might concentrate on their own frame design but use someone else's engine, shocks and wheels. This might be crucial or not, depending on how good or innovative the company were.

Things to consider, then, are:

1) Prices of bikes of comparable manufacture, age and cc.
2) Mileage
3) Condition
4) Availability of parts

A bike is, primarily, a working machine so all of the above are really first considerations. Only after that should you consider things like 'rarity', 'collectability' and so on. When you get into that league, the most important criteria are:

1) Original condition (that is, how much is the machine 'as it came from the factory'?)
2) Overall condition (i.e. how much is it going to cost to bring it to as nearly 'as new' condition as possible.

The existence of an enthusiast's club (site) would be a big help. I can't find one. Maybe your friend should consider starting one before selling in order to enhance the
desirability (and thus the price) of his bike!
2)

You could always check on different auction sites like Ebay. Also maybe there are certain kinds of books on the internet that may have the information. You can also check out the library.

You might try looking for vintage motorcycle groups and through them contacting people who might be able to give you the information that you want. But as owlwings says, the value of the bike really depends on the condition and on the interest that people have in the bike. Especially the latter as is essentially a enthusiasts market that you are dealing with with bikes of that vintage.

The way I see it,, the condition of a vehicle is important,, to find a price for it,My old bike looks so nice I might get more than what I payed for it,,This is my experience with another I sold a while back

Well have you tried ebay, i think this might be useful, if not try..
Thanks for sharing.
Welcome always.
Cheers.
Professor

hi bwrattybaby why not try the America Antiques Road show Pbs as its on our mylot search bar to get the www address as they have all kinds of antiques and motor bikes i am s ure are included. so do
try that site just type in America's Antique Road show PBS and you will get the web site addy. hope this helps.