Someone had discs on sale for cheap recently. I'll look for a link. IMO it's not a lot of work (bolt up the calipers, swap the levers, and throw the old brakes and levers in a bag). I just got a mtn bike built up and it's my first set of discs. So far I like them a lot, but they'll take a bit of getting used to since they're hydraulic. Mech discs are fine though, and I'd choose those if I were you.
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Current Stable: Trek Emonda SL - Trek Top Fuel 8 - Scattante XRL - Jamis Dakar Expert - Trek 9700 - AlpineStars Al Mega