1. Online Marketplaces: Search online marketplaces like Reverb.com, eBay, or Craigslist for similar Gibson RB 250 banjos. Compare the prices of these banjos to get a general idea of the market value.
2. Vintage Guitar Dealers: Reach out to vintage guitar dealers or luthiers who specialize in Gibson instruments. They can provide an expert opinion on the value of your banjo based on its condition, age, and other factors.
3. Gibson Serial Number Lookup: Visit Gibson's official website and use their serial number lookup tool to find information about your banjo. The serial number can provide insights into the year of production and other details that may affect its value.
4. Appraisal: Consider getting an appraisal from a professional appraiser who can physically examine your banjo and provide a written valuation. Appraisals can be useful for insurance purposes or when selling the banjo.
It's important to note that the value of a Gibson RB 250 Banjo can vary depending on various factors such as its condition, year of production, modifications, and provenance. It's recommended to consult multiple sources to get a comprehensive understanding of its worth.