Nomihoudai are economical and great if you are in groups..

Normally Nomihodai are timebound. It is for 60 min or 90 min or 120 min etc and this is told /decided initially when you enter the shop.
There are set of drinks which you can have as much as you like in these 60 or 120 min. Drinks not included in this list have to be purchased separately at normal price. So do check which drinks are included - else negotiate for the same initially itself. Drinks normally included are beer, housewine, gin tonic, shochu based drinks etc. Hard drinks are not included in some places while in some places one can find so.
These days there is a range of 980 - 2500 JPY approx. (std around 1750 or 2000) for this all you can drink type places. The idea is that once the customer comes in they will order something else as well.
Around 10 or 5 min before you finish the 60 min or 120 min time, the hall staff is supposed to come to you and tell that this is a last order and after that any order will be at a regular rate. This is a signal and one can order last few drinks before the set time finishes off.