i'm not sure if "harder/more difficult" is truly the issue with nanos. i think it's more a question of vigilence. the main thing you MUST keep an eye on is varying parameters on a nano because of the much smaller volume and quicker change in levels from the smaller ratios (especially salinity from evaporation).
you could start a nano with a couple of hundred bucks. the main cost will/should be your lighting.* the quality of your lighting will basically determine everything else down the road. imo, if you spend it once and go all the way, you won't spend 3x or more to finally get to where you want to go. i.e. get a metal halide setup. the aesthetic look alone will be worth it imho.
other mandatory stuff: don't skimp on the salt either but it's an almost negligible cost factor for nanos. water shouldn't be skimped on either, go distilled, RO, or RO/DI (or NSW if you can get it). test kits, refractometer/hydrometer (get the former), heater, and good quality LR.
optional stuff: good protein skimmer, live sand, additives, refugiums, and other fancy do-hickeys.
you'll need (imo) powerheads/filters but that's also dependent a bit on your aquascape. i'd get one microjet (or similar) but hold off on the rest until you see what your rockscape actually looks like/turns out to be (your own rock placement skills).
*lighting may not be ultra important. i'm contradicting myself here because i'm personally in the middle of an experiment involving a 2.5-gal. pico reef using only natural sunlight. 3-months, so far so good. not a recommended setup but i wanted to be completely upfront.
