The tank you can get for $10 at *****
Dollar a gallon sale (you might consider a 20 gallon you'd have more options).
A hob filter would probably cost around $30-50 Same for a heater. Depends on quality.
A light fixture for fish only can be anything. And wouldn't be very expensive there are some LEDs that aren't too expensive for a small tank. You can still get the discontinued Kessil 150s at Amazon for $160 this would allow you some corals. HOt5s are always a good option, bulbs are around $20 and need to be changed every 9-12 months. T5 fixtures can be found on eBay they are cheap and come with bulbs, not good bulbs for coral but you can change them out for high quality bulbs when you are ready for coral a few months along.
You will need at least one power head. I'd recommend Jaebo RW4. About $40-50 on Amazon. Great pumps that are controllable so you can set speed and even on and off to mimic waves.
You will need a refractometer and calibration fluid. About $35-50.
You will need test kits for ammonia nitrite and nitrate to start with. Stay away from API, seachem, Salifert, and Red Sea are all good brands. These are usually $20-30 each but you can find master kits that contain several in one which is a better deal.
After your tank cycles you will need others Calcium, magnesium, Alkalinity, and pH.
Sand for a tank that size would be about $20
Rocks can be pricy but are essential. I usually buy dead rock at bulk reef supply for about $2.75 per pound you'd need about 1 pound per gallon. I'd also get one small live rock from a fish store to seed the dead rock. Live rock can be expensive, around $10 per pound where I live.
If it were me I'd also invest in another small tank and a sponge filter and small heater to use as a quarantine tank. You don't want to add any fish into your main tank unless they are healthy. That means at least 30 days in a QT tank.
Eventually you may want a HOB skimmer as well. Not necessary or needed until your tank has cycled. Cycling the tank is important an can take anywhere from a couple weeks to a couple months
There are a lot of options with varied cost and quality. I'd research the products and shop around.
I'm sure I have missed some things. It isn't a cheap hobby, but very rewarding.