4spd - the lathe is probably going to be a better investment from the standpoint that many of the parts that you could make to augment a car or truck project are cheaper to make yourself on a lathe than a mill.
Case in point - if it is a 2D part that can be made on a mill, it can also likely be made on a waterjet or a laser. I have had disk brake brackets made on a laser table in canby oregon for less than $10 a bracket - cheap enough so that when you figure out you shoulda done something a little different, it is easier to toss the brackets in the scrap bin, redraw the bracket, e-mail the file and just have a couple more brackets made - from e-mail to your door in 3 days is typical. Once you get in this mode, it is amazing how many inexpensive parts you can "make" constructed from flat parts cut on a table. (You should see my shop sink surround out of stainless
)
Turning on the other hand always involves a setup charge and you have to spend a lot of time detailing surface finishes, radiuses, etc. and if you screw up on the drawing - it is still expensive! I would get the lathe first . . . and if you want to put any kind of DRO on it - drop me an e-mail and I can set you up cheep as I have a lot of surplus stuff laying around from machine tools we have retrofitted over the years.
