There’s countless threads on here about the cost and time needed to build your own splitter, if it’s something you want to take on that’s great. But most will spend more time and money than just buying.
I agree with the more expensive to build than to buy statement on entry level splitters. The costs of new components alone for the $700-$1200 splitters at big box marts are more than the cost to buy the complete splitter.
However if you buy good used components, score some free parts, and only have to buy a couple of new parts (available on eBay and Amazon for much less than retail) you can easily get under the $500 mark.
Now you still have to have the time, knowledge, and tools to build it right. You also have the freedom to move away from the basic design used on entry level splitters.
I broke my welder a month or so ago before I got my splitter together and I am putting the finishing touches on my welder today. After I get my skid steer bucket welded up and my yard put back together, I will get back to my log splitter build. I should have around $1000 in it, but it will have a 18 hp engine, 22 gpm pump, log lift, and possibly an adjustable 4 way. This steps it up to a much higher class log splitter for the cost of an entry level splitter.
I am not bashing the splitter companies, nor people who use their splitters. If you are happy with a big box mart splitter, and the company is making money, then capitalism has done it's job. I however want designs on my splitter that are not made by any major manufacturers, and can not afford a custom built splitter from a small company. Even simple things like work height can be set to fit me during the design phase so I have no need for ramps or boards to raise it.