Robbie sells his instruments at SL Boutique - a steel drum set costs L$120 (40 cents in real money), while a Hyper Flute costs L$3,000 (around $10). Most Second Life instruments are really toys -- they'll play a couple of sound loops and animate with your avatar. Some are slightly more advanced: Robbie's 1965 Fender Stratocaster (L$400/$1.40) "loops a funky pattern that can be transposed via the menu system to any key whilst remaining in time." How many real-world guitarists can say the same?
Robbie's greatest claim to fame was creating the guitar used by folk singer Suzanne Vega when she played a gig in Second Life. As far as I can work out, the guitar in this case was just a prop -- she was playing a real guitar into a microphone, whch was beamed into the concert.
Other SL gear manufacturers include Neurocam Audio, who produce headphones and microphones, which really confused me. How does a microphone work? It "serves a purpose: It changes your chat to GREEN in the chat window, allowing the event host the ability to be noticed above noisy crowds!"
Finally, for just L$1 (1/3rd of a cent), you can buy a Cigar Box Guitar, just like the one featured in Make Magazine, which will play a short clip of cigar box guitar jamming. Virtual cigars not included.