First, the benefits of DIY subs are greater than DIY speakers! Consequently, if you have any interest in a sub, I would start with building a DIY sub and use that as an introductory experience to DIY speakers.
DIY Subs have several advantages as a first project:
The cabinet is large so the cost of the cabinet (and associated shipping for such a large/heavy item) is a greater percentage of the total cost.
Generally you but a plate amp or a pro-audio amp which has the crossover adjustment built into it, so no crossover/soldiering.
Subs are usually flat black and are not so much on display so a finishing SNAFU will be less of an issue as compared to speakers which are normally in plain sight! Also, the same goes for mistakes in the joinery. With modern glues, you don't have to have all of your fit-ups perfect to have a solid box, but from a cosmetic standpoint, you want clean match-ups between panels.
Once you've built your first sub, you will have a much better sense of the important questions, which are things like:
How much pride do I get from saying "I built that"?
How methodical and careful am I in construction of a woodworking project like this?
How much patience do I have for getting a good finish after the box is built?
As mentioned, you can get a kit which is really a simple assembly project. Even pre-built and pre-finished cabinets! Of course that cuts into your saving from DIY.
For speakers in the sub $500 range, I think there are enough occasional deep discounts on them that if you have the patience to wait and keep your eyes on the "Deals, Deals, Deals!" sub-forum here, you can get a manufactured speaker for the same price you would pay for DIY parts for equivalent SQ.
If you have patience and expertise, you can also do very well keeping an eye out for used speakers via CraigsList! The expertise comes with time, but if you are ready to buy and post a link here to your local Craigslist, there are several of us that enjoy the "treasure hunt" game of seeing if there are any bargains. Of course you will need to evaluate condition, but we can offer advise on that. CraigsList has the advantage that you can listen before you buy; however, if you are just starting out and don't have experience listening to good speakers or (ideally) the real sound of acoustic instruments, any competent speaker is likely to sound very good!