You know I'm still learning about them all. In some of my searches I have seen very expensive coral! Is this hobby one that can be done on a budget ? :-/
Depends on what your perception of budget is? This hobby is near limitless on upgrades. You have an existing tank. You will need a gyro or wave maker for waterflow. Maybe a hang on back skimmer and lighting better suited for coral.
http://www.LiveAquaria.com has everything categorized. Not all coral are expensive. Compared to freshwater plants and fish? yes. This hobby is expensive but is rewarding also.
I came from years of freshwater experience. I will say, it's easy at first. It's really nice how your CUC or clean up crew helps take care of the tanks clean appearance.
Your shopping list for a budget tank could start with
25-36lbs Live Rock - ~$180 +/-
1 or 2 bags of dry sand - $30-$40
1 HMO-150 Finnex Heater 150watt -$33.29
2 Jebao RW-4/PP-4 - $100
165W MarsAqua Dimmable LED Aquarium - $85 to $95
Aquamaxx HOB-1 Skimmer w/ bubble stopper -
On Sale $191.98 (marinedepot)
Test kits - $45-65
Estimated cost = $675.27 (price doesn't include food, coral, fish, auto-top off system)
**This is just an example**