For kits with longevity, the Parts Express BR-1 just seems to stay around forever. It's been available for at least 15 years now. I don't understand why it is nearly double the cost of the C-Note...
I look at the C-Note as an interesting benchmark for DIY projects. It is a complete kit for 100 USD as the name implies. For that price, you get a pair of flat pack cabinets very similar to blank ones Parts Express sells for $50/pair. A pair of the woofers is another $50. The woofers make decent bass in that 7 liter (approximately) enclosure. The tweeters are $40 and have small waveguides that should at least help some with directivity. Add in the crossover components (about $60 retail I am guessing), port tubes, binding posts and the kit is an obvious value and challenging for the DIY'er to compete with. The speaker preference score vs. price chart illustrates that fact.
If I were just picking out equivalently priced drivers, I think one could do better, but one would need to do considerably better given the level of discount for the C-Notes. I would be confident putting my Mercury project up against it (7L cabinet, HiVi M5n woofer, Vifa BC25SC06-04 tweeter). Drivers are actually $25 cheaper, but crossover cost probably gives that advantage back. Reviewing my bill of materials, I would be at about $205 with flat pack cabinets. There are a few other woofers that could produce similar bass extension in the same enclosure that might allow a simpler crossover, but it's difficult to envision getting below $150/pair including the cabinets without major concessions in sound quality.