I just went through OW 2 monthes ago, here is what it has costed me:
OW class from LDS: $295 (include $145 pool/classroom/rental fees, $150 instructors fee)
PADI course material: Costed me $50 because I shared some item with my buddy. Otherwise $100 if you buy everything as package. IMHO, most of these items are waste of money or one time use thing. If you have friends did this before, borrow as much as possible from them.
Basic gear: mask, fin, snorkle, boot, glove. I am sorry, I didn't support my LDS, I went with Leisurepro expect the mask. mask ($75), fin($125), boot (6.5mm $40), gloves (5mm $30), snorkle ($20). Total costed me about $300.
So far, costed me $750 to get OW cert.
One of my LDS offer daily rent at $35/day for 1 tank, reg, bc, weight, wet suit. If I dont buy anything, it will cost me $35/day of diving from now on.
After a few dives, I found bouyancy control is one of the most importnat thing in water. And since rental offer me different BC and wetsuit everything, I decide to get my own BC/wet suit/weight.
BC: BP/W + misc items, ~$550
Wetsuit/hood: $180
Weight/belt: ~$70 ( I didn't know lead can be this expansive)
so this is another $800 in equipment (total $1100 in equipment). I still need to rent reg and tank everytime I go, so that is about $15 per day.
Diving is definitely not cheap, but compare to hobbies like photography, goft, sailing, I actually think it isnot too bad.