I think I'd go with configurable products.
Create the event as a configurable product. Each slot/price level (I'll call it ticket category for my explanation) is a simple product which isn't visible individually.
(I hope I understood what you want to do. I imagine something like a concert or sports game with tickets for seats in different categories, e.g. first row or second tier. Could also work for a conference with a one-day pass, two-day ticket and so on.)
My reasons for this decision are:
- You can group the tickets for the event using standard Magento methods.
- Each ticket category (price tier) has its own inventory out of the box.
- By checking the cart/order history for the simple products associated to the configurable product you can put restrictions on the quantity of tickets which the customer may buy.
- By overwriting the price calculation method for simple and configurable products, you can have very flexible pricing. Special, group and tier prices can be available on a per-ticket-category level. The UI is ready for your client to enter the data so this isn't a huge deal.
- As each ticket category is a separate product, you can make available much information based on the ticket category. Think additional descriptions, images and so on.
- It's pretty easy to adjust the product page and have the customer buy tickets for different categories at the same time without reloading the product page.
Update after sparcksofts update regarding the type of event ("boat trip"):
As Petar said in the comments: normally you'd manage inventory on the simple product level. The flexible quantity of the price tiers changes things a little bit.
You could handle inventory manually (= not use the standard auto-increment/decrement from Magento).
If only one price tier can be purchased at one time, you could set the inventory stock to the same quantity for all simple products when one price tier is purchased.