How did you arrive at 15k? For personal use, it's common to get aftermarket 3090's, link them up four-way (96 GB is not half-bad) and put it in some server motherboard with as many DDR5 channels as possible... imho in 2025 this is a total waste of time, but it's possible, and at a fraction of your estimated cost... Seriously though, H100's go for $2/hr these days. I personally spot g6e.48xlarge (384 GB) which goes for under $1. Why bother hoarding many years out-of-date hardware which is like running three washing machines all day...