Well, personally I will not advise to go for the cheapest.
There are few things that you should ask when u walk into a dive shop.
1) Is Padi Manual given to you or just on rental
2) Are there any hidden cost such as equipment rental
3) Destination
4) Instructor to student ratio
A PADI Manual is a book on the dos and don'ts of diving. It is a guide book that can come in handy when u have not dive for a long time. You can use it as reference.
Some dive shop will charge you $300 for the course. But that is not the end of it, when u are about to pay, they will pop the question if you have your own diving equipments. If not, they will charge you extra money for it.
The three most common dive destination, Aur, Tioman and Dayang. Each has their own pricing. So check with them your destination and the resort you are staying at. In Tioman, there are different grades of resort. And since you are going with a girl, ask them if they have twin sharing rooms
Last but not least, the instructor to student ration. Recommended ratio is 1:4. The smaller the group, the more attention will be given to you, hence u learn better.
My personal experience is to go for a good open water course and learn well, especially if you plan to be a frequent diver.
Let me know, I can give you more advise.