You should look into all that is involved $$$ wise because this is hobby really isnt for anyone on a tight budget.
Its best to do things the correct way and not the cheap way.
You need to decide what kind of tank you want to have, reef or fish only... A reef is alot more $$$ then fish only.
You will need a tank, a stand, and a protien skimmer is a must... Since you want to keep it cheap youll probally need a mechanical filter also instead of buying a lot of Live Rock at $5.00 + a pound. You will also need some power heads for flow... Depending on if you want a reef or fish only tank determines how much flow is required.... 10 x's turn over per gallon an hour for fish only... 20-25 x's turn over for a reef.
A reef will also need expensive lighting.
What size tank are you setting up?
Then theres getting pure water.. (dont use tap water) either buy RO/DI water by the gallon , or buy a RO/DI unit.