Part of the price is for the brand name, but the quality really is different from your standard AGA tanks. Honestly, I will agree that most everything else IS overpriced, but not by much more than other products that would be close in quality. If you don't want to spend the money for pipes and the lights, you could check out Cal Aqua pipes (available at GreenLeafAquariums.com). Many people use those alongside their ADA tanks, and they work well together. As far as lights for a nano, nothings going to mesh as well with a Mini-S or Mini-M as their respective Solar Mini, but a pair of Ott-Lites (search Google I don't know where these are carried) will do the job well, along with looking pretty nice. Another suggestion is the much used 27W Hampton Bay Desk Lamp, which has also been called the "Nano Light" or my favorite, the "Robocop Light". IMO it doesn't go as well with the tank as the others, but its only $22 and is available at Home Depot (it's not listed on their website)
As far as all the other aspects of the tank I'd say defiantly get Aquasoil as your substrate, IMO its the best out there. The ADA Co2 is a little overkill, you can put together a great system with a larger cylinder for around $150, maybe even less if you find the right deals.
To sum it up, there are alternatives, like Cal Aqua and Ott-Lite for the really pricey stuff, Aquasoil will be the best bang for your buck, and building your own Co2 will probably be the cheapest route with the best results. But nothing beats a full ADA setup as far as looks go.