Meh. It's not like they're taking someone's money without permission. It's like a charity. They don't make you donate.
They might be thinking there is an adoring fan out there willing to fund them for things they need on their next album. I helped fund an artist once for that, the band was Einstürzende Neubauten. Although I got a CD out of the deal so I'd hope the funding parties get something for the money.
I find it a little hard to believe someone needs a custom instrument for that, that seems a little distasteful. However if it were someone asking for a mid-range model because they didn't have a bass, or their bass broke, well, it's fair game IMHO.
The only time I really have a problem with panhandlers is when they're aggressive or ungrateful. Who knows what sort of life circumstances led them to the place they're in. Im sure any one of us could have something bad happen where we're desperate enough to beg. People who are hungry don't put a higher priority on pride, which is understandable in my opinion.
I saw a woman the other day who was panhandling with her 1 year old. She was apparently staying in a shelter for women with children. I got to thinking, maybe the guy she was with was a wife-beater and she is just doing her best to make sure her kid is safe and has what they need.