It's almost always cheaper to buy a splitter than to build one unless you already have several of the major components.
ie, Even if you have the cylinder, pump and engine, you'll still need the beam, axle, spindles, wheels, tires, bearings, hydraulic tank, hoses, control valve, push plate components, wedge components, hardware, weld rod, paint, hydraulic fluid, hitch coupler, safety chains and so forth and so on.
I would recommend some planning and math calculations before anyone "starts" on a project like this without the knowledge of what the end cost will be.
I think a good option is to buy someone's failed project or perhaps a splitter that is inop. Repairing one will be a lot cheaper than starting over.
I know many of us are "do it yourself" type people and want to build a super duty, unique, custom splitter but...