Getting into K-On! inspired me to finally buy a new guitar after pondering doing so for almost 10 years. Watching the series inspired me to check out Gibson Les Paul Standards and I absolutely fell in love with the tone and feel of them. Even if I wasn't into the series I would've loved the guitar as they are some of the highest quality guitars Gibson makes that any guitar player can appreciate.
So I incorporate a $1600 "guitar prop" in my Yui Hirasawa cosplay. Throw in her backpack style guitar case ($40), her navy/light blue school bag that I had to order from Japan which is very useful for lugging guitar accessories ($70), and my portable guitar rig (portable Pignose amp $70, Boss RC-30 loop station $270, octave pedal $70), my "props" alone run to nearly $2000. The costs of her winter and summer uniforms and custom HTT T-shirt I made are insignificant compared to this.
I love playing guitar and cosplaying as her allows me to play music while being in character for a series I love. I also get a ton of use of these "props" when I'm not cosplaying so it's not like they gather dust outside of cons.