Ok this is how I successfully taken care of leopard geckos.
10+ gallon long tank, a baby and juvenile will be happy in this a adult is better of in a 15+ gallon long tank, don't use a tank bigger than 40 gallons, since it might cause problems with the geckos finding the warm and cool side. ($15-$80)
3 hides or more, each hide big enough for the gecko to get in, one hide in the cool side, another in the warm, and a humid hide towards the warm side (around $25)
Under-tank heater ( UTH), one that covers 1/3 of the tank. ($15-35 depending on the size of the tank)
Water dish, ($5-$10)
Substrate I use non-adhesive clean shelf line, it very safe and it looks good( $10) you can also use paper towels its cheaper but it does not look good, or tiles they look the best but are a bit expensive, those are the only substrates I recommend. (NEVER USE CALCIUM SAND)
Thingy to take the humidity and a thermometer I recommend a food/meat thermometer, so you place it anywhere and it take the ground temperature not the air. the ground temperature in the war side should be around 88 f and in the cool side 70-80, humidity no more than 50%.
Above the uth I put extra layers of substrate so the temp does not rise very high, and so i don't have to buy a thermostat which runs about $25 and up.
For food, I buy crickets gutload them with fluckers cricket diet and fluckers yellow quencher, and mealworms I gutload them with lettuce.
Also you have to buy calcium and vitamins which cost like 20-25 dollars.
good luck, and don't forget to pick a best answer..