It is entirely possible to build a speaker that will easily outperform a commercial one for the same money, though it may not look as nice.
There are many designs available by great designers that provide the volume of enclosure required, the crossover schematic and the names of the drivers to use. To get them to sing the box can be really heavily braced and battened and the parts for the crossover can be upgraded.
With a commercial speaker there are many constraints that prevent them from sounding as good as they could. If the cabinet was braced and used lots of timber to quieten the walls then the volume of box would by necessity increase to accommodate the extra support. This then makes for heavy and expensive shipping and together with the extra size makes for a less attractive sale. Also the XO parts are chosen to 'do the job' so the components will be reliable but rather pedestrian in sound.
Even expensive speakers use low priced parts. For example the series tweeter cap may cost $1 each but for your DIY units it's not that much of a stretch to pay $25 each. So a good design, stiff cabinet and carefully chosen XO components and you have a fine set of speakers.
Someone mentioned using a prefab XO. This definitely is not the way to go. The XO is the heart of the speaker.
Another approach is to buy a classic like the Altec Model 19 This is a brilliant speaker which can be improved by reinforcing the cabinet and rebuilding the XO. The battens to stiffen the rear panel should be mounted outside to avoid changing the port tuning. Just keep all values the same but avoid those nasty cheap white sand cast resistors and consider having the XO outside the box. Use low-mass speaker terminals and wire internally with single core OCC copper.
There was a thread that went on for years: 'the econowave' there is tons of info and reviews of various builds. A properly done speaker using a waveguide with a compression driver is impressive and IMO far superior to the ubiquitous me-too box with dome tweeter. Also many out there using the SEOS waveguide which measures as good as anything available with excellent measured performance. The transients from this type are startling and dynamics scary.
Remember Pink Floyd don't play through no stinkin' 1" dome tweeter. 😁
Try this: