It dates from probably sometime in the 1860s. Mulford & Biddle were jobbers who sold telegraph equipment in New York City and they had insulators made for them. UPRR is (as you probably know) Union Pacific Railroad, who probably contracted with Mulford & Biddle to have them made. These also turn up in cobalt sometimes, and if I recall correctly there is one green one known.
Price is hard to guess given the condition. Some people like the surface hazing/sickness (which is very common for this piece), while others prefer it tumbled. I've seen similar ones in the 150-200 range.