+1 for buying a good used bikes. I think bikes depreciate faster than cars price wise, but slower than cars function wise, and there's no reason that if you're patient and ready to pounce, you can't find a good, used 5 yo bike for 20-30% of new, with pretty much identical performance. A semi pro golf buddy said sports equipment depreciates so fast, because in essence, the 3rd best gold club on the market is as useless as the 100th best. If you want to win, you need to get every advantage you can. Fortunately, if you're *not* a pro who races, you can get an older bike with great absolute performance for a song because you're more concerned about a bike that goes fast and is light, than the fastest bike out there period.
(A slight aside, but in Australia, they repurpose old America's cup level sailboats for tours as once the technology improves, you can't win with them so their useless for racing. But they're also not outitted super comfortably for cruising either. But if you want to zip around at 17+ knots sailing + see some sights, a good opportunity to do so)
Learn how to do bike maintenance yourself, upgrade or adjust parts as needed, many cities have community bike shops which take donated bikes, repurpose them, resell, them, or strip parts, plus provide work space and all the tools, so check that out.
My main daily street and trail bike is a 6 yo Trek 7.5 FX which I picked up for $200 CAD last winter in the off season. Had to put about $150 into it because the non-mustachian I bought it from switched it to a single speed after breaking the derailure and not having the money to fix it, and also being eager to sell for XMas money, but given that it was apparently $1100 US new, and with $250 upgraded wheels. Easily worth $700 now if I'm patient, which would still be a steal give how it performs. I mean you can replace ball bearings, replace hubs if needed, new chains and sprockets. All cheap lightly used, and there is simply nothing like a head gasket or a blown transmission that will totally fuck a bike (short of a bent/cracked frame) you can't learn to do yourself in hours.
It's the classical used vs new debate, but there's no way I would equate even a 10 yo depreciated top end bike that's been looked after to be the functional equivalent of a mid range wal mart bike new, but I don't set the market. I suppose liquidity is the other issue as well though. Great bikes for cheap, or even reasonable prices don't show up often, and often don't last.