Micheal Angelo was able to carve huge statues out of marble with nothing but a hammer and a chisel, the only limit is your creativity. everything I use a mill and lathe for now I used to do with a drill a grinder and a dremel. tools make the job easier and faster but you'd be surprised how much can be done with just basic tools
True enough, but if Mike had a mill and lathe we'd all be whipping around in hover cars by now
For the longest time I built using only a DP, batt drill, Dremel and an soldering iron, and the best tool in the world, the glue gun

...it forces you into finding some creative solutions and techniques that I still use even though I've built up a decent collection of tools.
i.e. when performing my chop/channel job on my Lancia I found it faster to simply chuck the pins in my batt drill and hold the Dremel/grinding disc against them in my Den then go out to the shop and use the lathe...the end result is pretty much the same on an operation like that.
However, now that I've had the first full weekend with a lathe, I will say, I can see the potential of that tool is enormous, but, having said that (and this is totally personal, and most likely born out of the style of
mod I like to build)...if I had to give up either the lathe or the mill...no contest, the mill for the win. I look at it this way, both are very accurate rotational shaping tools, the lathe is designed to rotate the work, the mill is designed to rotate the tool. In our world of box mods (generalization) rotating the work can be impractical.
...just my opinion, but if you can only scratch together the loot for one at a time (like me)...I'd start with the mill...a lathe is a very useful luxury