I've made a couple of mandolins and a 5 string banjo from kits, all of which sound and play pretty well, at least as good as anything "commercial" I've heard or tried new. The mandolins in particular were very cheap, these were made from kits from International Violin (look under the "White instruments and kits" section). There are certainly prettier instruments out there, but my kit mandos and banjo have become my main instruments and have greatly surpassed my expectations. They were also interesting and rewarding to make.

I've also made an Electric Mandolin of my own design which IMHO wasn't half bad at all.

Not yet made any acoustic instruments but there are several in the pipeline, including gourd banjo from scratch (if we get a long enough summer to grow a decent gourd), and several conversions/hybrids including a short-scale 5 string banjo using a banjo mandolin pot and an old 12 string guitar that will eventually become an 11 string fretless guitar-oud. The only problem is finding the time - work keeps getting in the way!

I'd strongly recommend having a go - but beware as it can become an out of control hobby!

Pete.