Guni's examples are great, I'll just add some extra information to it.
됐거든 is an ironic expression to mean you refuse to take anything worthless such as a lame excuse, bad joke, big talk, patronizing offer etc.
되다 is probably the most idiomatic verb, it means:
1. It's completed.
(B is fixing A's broken computer)
A: 아직 멀었어?
B: 다 됐어. It's completed.
2. It(or everything) is okay.
(after making a lot of effort not to apologize first)
알았어. 미안해, 내가 생각이 짧았어. 이제 됐어? Okay. Sorry, I was careless. Is everything okay now?
*이제 됐어? could put you in trouble if you say it in a situation where you did something wrong.
(B is sulking)
A: 삐졌어? Are you sulking?
B: 됐어. It's okay. (a pouty expression on her face)
2. It's ready.
- 저녁 다 됐어. Dinner is ready.
- 다 됐어. I'm all set.
3. (Time) is up.
시간 됐어, 가자. Time's up, let's go.
(A's being caustic)
B: 됐어. 그만해. Enough. Stop it.
Essentially, without an object 되다 means 'to become(reach) something ideal/ultimate'. So it is used as those above. Let me take another example, we say "못 됐어" when talking about someone nasty, meaning they didn't reach a certain standard that we think people should.
-거든 is used to inform someone of something. With 됐거든, you're speaking as an informant. "I inform you that it's okay", but it's not okay in fact - this is why 됐거든 sounds sarcastic and a bit cynical at times(with your tone, facial expression)
됐고 sounds neutral.
- 됐고, 잠이나 자. Enough, just get some sleep.
됐네 sounds friendly.
이제 된 거 같네, no? ^_^