1st: Buy used! The rate of people dropping out of this hobby is astronomical. There are _always_ high quality, nearly new systems being broken down and sold off. On this forum, look for a local reefing group... lots of sources.
That said...
Lighting. T5 lighting, which can be found at a reasonable cost (especially if you pay attention to item 1!) is a perfectly acceptable alternative to spending several grand on the latest high end LED lights. I bought a used 4 ft 8 bulb TEK T5 light that (IMHO) looks _better_ than the new ATI T5's (Chrome? Really?) . Put new ballast in it, polished the reflector a bit, new bulbs... it's working very well, thanks. Total cost for lighting my 60x30" tank? $325. I could have bought 3 Radion 52's + mounts, for what, $2500? Wouldn't have grown corals any better than what I have. Number one place to look for value... lighting. It's a critical component, but high end lighting is not, IMHO, worth the price difference.
Things _not_ to skimp on:
ANYTHING that you're going to have to look at every day. A nice looking tank on a rickety 2x4 stand is an eyesore. Build/buy a stand that you can be proud to own, and you'll own it for a long time. Throw something together cheap, and you'll be sick of it in no time.
Items that are going to require regular maintenance: Skimmer, ATO reservoir, media reactors (I actually like the BRS dual reactor...) You'll be spending time cleaning, changing, etc. on these constantly. Don't get something that is going to be a pain to maintain.
Critical single point of failure devices: Heaters, for instance. Can't tell you how many tanks have been killed by a cheap butt heater. Buy a decent one. Better yet, plug a decent one into a Reefkeeper Light... then you've got some redundancy. Watch BRS's video on heaters, and the one on using the reefkeeper light and a heater. ATO systems, I won't buy anything but Tunze ATO's any more. It's a prime culprit in system failures, floods, etc. Power strips: Don't buy a $5 wally world power strip to run your expensive aquarium.
And... the number one resource in this hobby... TIME. Nothing good happens fast, and the learning curve is steep and broad. Take your time, and ENJOY the process!