Some things to think of
1) whose copyright will software be ? If his you will need to supply source, if yours then he will need an ongoing support agreement.
2) is your customer expecting this to be a bespoke system ? In which case cost will be high, because it must cover your costs and give you a profit.
3) how long will it take you to develop ? This helps to determine your costs.
4) are you going to sell it to him or licence it ? If the latter then you need to find more customers or you won't make any money.
5) Do you know what his budget is ? (no point in exceding his budget)
Out of interest why not use a relational database, such as SQL, access, etc ? It sounds like a stright forward database application.
Hope this helps - any questions come back