Hi ive got some info for you, Prince pellets were made by "LANES" (Charles Lane) of victoria St London, he produced many pellets under his own brand name, but also for a variety of other manufacturers.
His own pellets include
1, Lanes Bango
2, Lanes Cat slugs,
3, Expanded bullet No1 Gem
4, Lanes Heavy weight
5, The Perfect Bullet
6, The Rotary Bullet,
7, The Triumph,
8, Japanese Jet
9, Silver Jet,
!0, The turbite,
And more, all of the above are airgun pellets/slugs, produced from (approx) 1901 until the 1930s. The value depends on which ones you have, on average, they generally sell for £2-£3 per box.