There are a lot of price guides and websites devoted to records and record collecting, but not as many devoted to music items beyond vinyl.
One resource though is the website: MemorabiliaRocks

MemorabiliaRocks looks at music memorabilia such as — sheet music, guitars, clothes and ticket stubs.
It also looks at genres like hip-hop and jazz and tells you if specific artists like Frank Sinatra or REM are worth collecting.

So if you’re a collector of music paraphernalia, then I urge you to check out MemorabiliaRocks.