What he said. Sadly, CRTs are pretty much "out of fashion now", including most of the iMac G3 models, meaning that they sell for quite little and even go for free. Your iMac is worth more though because of the upgrade.

Incidentally, for collectors, now is the time to pick up G3 iMacs as they are available so cheaply and will probably become quite scarce within the next decade. I can see them being quite a "retro novelty" about 20 years from now.