Lots of factors involved in determining values for scrap metal:
1. Metallic composition of the scrap (cartridge brass in the US is typically 70% copper, 30% zinc, but that formulation is not fixed and foreign brass may be substantially different).
2. Quantity to be transferred. A scrap dealer is likely to be far more willing to pay a good price for tons than for a few pounds; total profit for the transaction may not be worth the time and effort.
3. Distance from the scrap location to the foundries that may wish to be the ultimate purchasers for re-use in new metal products. Transportation costs mount up quickly when tons of materials are being shipped longer and longer distances, and the local scrap dealer must take this into account when determining how much to pay for what you have to offer.
4. Local or state laws pertaining to scrap metal dealers. In some areas the dealer may be required to report each transaction to authorities (a means for suppressing thievery), perhaps hold each purchase to permit law enforcement to correlate to reported crimes (metals markets can be volatile, and if the dealer is required to wait 30 days prior to resale there is increased risk for the dealer), sometimes detailed reporting (requiring time to complete each transaction report and forward to authorities), etc. All of these may impact what a local dealer may be willing to pay for your scrap.
Seems easy enough to look at the commodities reports in the newspaper to check prices for brass, copper, zinc, other metals, weigh out what you have to determine a fair market value. In reality, while you may have $100 worth of metal at market rates, the time and expense of handling and transporting to market may make your few buckets-full worth only a small fraction of that at the local scrap yard.
About 30 years ago I had an opportunity to purchase the entire results of rewiring a large coal mine, all light to medium gauge insulated copper cable. Location was about 125 miles from the nearest scrap dealer, and the dealer required that the insulation be removed prior to purchase. We chopped cable into manageable lengths, burned off insulation in a bonfire, then loaded onto semi-trailers using a backhoe, and had everything transported to the dealer's scales. Total involved was about 25 tons. After paying all expenses for labor and transport the profit amounted to $315 (less than $13 per ton). I would not do that again.
Best regards.