How would you do this (saving variables on WP)?

Ok so someone else was working on this and foolishly I've said I can help - had a closer look at the code and it's a total mess!

So there are six 'packages' on my site. When the user selects one it takes them to a page I've designed for each one. Let's say they click on 'package 1'. What I would like is to save a variable price let's say '100'.

On the next page is a form with optional extras where they can pick and choose from option boxes. The form then totals up the optional extras and saves into another variable optionalextras let's say '50'.

They hit next and they get another form which they need to fill with address details, name etc.

Hit next and then they get a summary of the variable price, variable optionalextras and a total price.

What's the best way to achieve this? The previous person working on it decided to save everything into the WP database for some reason! I'm thinking either session variables or maybe there's a plugin which can handle this nicely? Any help would be much appreciated.

Thanks