To get back to the original question.. is it cost effective to build your own splitter?
If you want an entry level basic splitter and you have to buy everything new, no. If you want one with a fast cycle time, log lift or hoist, catch tables, one with a little more attention paid to ergonomics, absolutely.
Price a splitter with an 18hp electric start engine, a 28gpm pump, 3/4" hoses and a 16 gallon hydraulic tank, and the $1500ish I have in mine suddenly got cheap. Now that store bought splitter will look much better than mine with much nicer paint or powder coat, the welds would hopefully look better and the whole thing would be more polished in design, but I bet you'll drop $3-4K on it. Personally, I wish I had the cash to buy one. They come standard with a lot of "Tim Taylor" grunts and such. LOL
Ian