As I mentioned in a recent post, I worked at a laser cutting shop for over 5 years. I handled quoting, designing, programming, running, fixing, and maintaining the lasers... ya, pretty much everything but not necessarily at the same time - well, ok there was that one day..... ;) I worked closely with other shops that we outsourced jobs to, including lots of waterjet.
There are many common misconceptions about how lasers work and what they can do. I probably won't do the topic justice in this short post but if you have some specific questions that I can answer, I'd be happy to do so.
If you're set on aluminum, and it's going to be more than 1/4" or so thick, your best bet is waterjet. You should get a nice clean edge that almost looks sandblasted. Likely a bit sharper on the bottom of the cut and a bit more rounded on top. Taper depends on many factors, bot a good 5-axis machine and operator can all but eliminate it. To get the price down a bit, they can run a faster travel speed with the tradeoff being a rougher edge. If you can live with a very rough edge, aluminum can also be plasma cut - but if you're to that point you might as well rough it out on a bandsaw unless you're making hundreds of them. Do consider more conventional, more manual options carefully until you're selling so many you can't keep up with the orders.
Lasers cut steel very similar to the way an oxy-acetylene torch does; they heat up a small spot to molten and with a constant stream of low pressure oxygen, burn it away out the back of the cut. Get everything just right and you end up with a very nice edge (not quite to easy to maintain in practice...). For aluminum, it's a bit different. Nitrogen is used at a much higher pressure and it's used to blast the molten aluminum out the back of the cut. Since aluminum is so good at conducting heat away from an area, it's very hard to keep the heat exactly where you need it. You need much more laser power for a given thickness of material.
Where I worked, quantity was everything. If you needed one or two of something, expect to pay for some setup time and a premium for material usage and other miscellaneous. Remember that when you're getting pricing. Maybe even ask them what they consider to be a "worthwhile" order. I'm sure some places will cater more toward prototype stuff, while others will be into production. Pricing will be more local, so my numbers won't mean much to you. Not to mention like I said it's quite variable depending on what you actually want done.
David is "spot on", DXF is the most common file format I received. 3D formats have become very common too, with IGES, STEP, and SolidWorks files being used directly. You're a lot less likely to get the wrong thickness part that way too.
I say get yourself a solid design first. You'll probably end up paying way too much for prototypes, and will have to make changes to them before you ever get into quantity. Along the way, you're going to learn a lot and will start getting a sense for what you need to charge for this item.
Oh, and do yourself and your brother a huge favour - make your design self-fixturing if at all possible. Your imagination and ingenuity are the limit, as long as you're also within the physical limitations of the machines you have access to.
