Does anyone have a schematic, or a resourse to help me make my own power adapter to be able to use my laptop in my car?

I just bought a older, low cost Powerbook 3400c, and it didn't come with an adapter/charger. I'd like to use it in my car at times, play music on it, like a iPod for under $100.

The specs say it needs 24 volts 1.875 Amps, and my laptop says the same. The AC adapter specs say it's 45 W. <>

Can anyone help me with a schematic or instructions to make an auto adapater for my laptop or tell me where I might find something like that?

The professionally manufactured power supply at around $40 seems expensive to me, I'm trying to save money.