If you have even half reasonable DIY skills, it is quite easy to make speakers from a kit: some of those by Wilmslow Audio are said to be very good. And if you have an interest in transmission line bass (for me the approach that sounds natural) there is a British firm called IPL that again have a good reputation. Using kit speakers the biggest challenge is the finish, where your DIY skills may be most needed. IIRC IPL and maybe even Wilmslow Audio have some of their models available to hear at their store, which would be the best place to start. At least one member on the old forum had built IPLs, but not sure if on the new forum, and search facility of archived old forum at the moment is inadequate.
There are also lots of speaker designs available just as the plans, from a huge number of sources: the biggest difficulty there may be getting any idea of which ones actually sound any good! You need to be prepared to have to do a lot of tweaking, or even abandon and start again - or you could be lucky.
You can also design completely from scratch and there are design tools available, for example to calculate certain dimensions etc, then you are in a similar place to picking up plans.
Unless you go down the active route with a fully adjustable digital crossover, as I have, getting the crossover right may be more difficult than the physical construction.
I have a project on the go, albeit dormant for couple of years, but for me transmission line bass is the only worth having, so I am designing a pair of those. The mid and top I decided to do using a satellite enclosure for various reasons, and that was no trouble at all and is now in regular use in my main system in place of the mid and top of the bought speakers. My first two attempts with the transmission line bass part, were less than satisfactory, and it has gone back to the drawing board. But then I have a high bar: they must sound at least as good as my PMC speakers.
It is certainly possible to make speakers sounding as good as or better than commercial speakers for less money, though I think the better the commercial speakers the harder it is to do that, as after all at that level they have put an awful lot into their designs. And whether you save money compared to secondhand speakers is less certain. For reference, my PMCs current equivalent to my model cost about £13K today - but you can buy mine secondhand for around £4K. The parts for my mid/top satellites cost the equivalent of about £1300. My active crossover cost about £1000 (a major part of that being the cost of parts for its modification from stock). My bass drivers cost about £500 for the pair, but I’m going to have to change them, so more cost though some recovery secondhand. Wood and other materials only a few hundred £. I guess that if I achieve it I will have paid a bit less than than the secondhand cost, and the mid/top certainly better. Many, many hours of work - but then it is a hobby, and great satisfaction at the end if I achieve the goal. If I don’t I will keep the mid/top, sell bass drivers, and still have better than where I started.