This is kind of a subjective question, and one that I wrestle with occasionally. The biggest factor for most people is their time vs money situation. If you have a lot of time and not much money, you will probably opt to build more tools, and vice versa. I am allowed a decent budget for my shop hobby, but I have projects stacked up out the wazoo, so if it is available and not unreasonable (I'm still cheap) I will buy it. But sometimes it comes down to capabilities and aesthetics. I am thinking about whether to purchase Tormach’s new lathe attachment that goes on the mill, or convert my HF 13x40 to CNC. The cost for either is very close, but the conversion would take much more time, but provide much more capability and I wouldn't have to swap it out on the mill when I want to use it. I still haven’t decided, the lathe needs work anyway, as I think every oil seal on it is leaking and I have to keep cat litter on the floor by the headstock to soak it up. I also have an old Craftsman lathe that I would like a stand for. I have located a roll around tool chest that with a few modifications would be a perfectly functional lathe stand, but it's not very pleasing to the eye, so I am contemplating building one (likely for about the same cost). Both of these build/buy choices are more tradeoffs between my time and either functionality or aesthetics, rather than cost. These are the decisions that I have a hard time with.