I recently put a 512GB NVME drive in my laptop (ADATA SX8200PNP) which was under £60. It wasn't the big change that swapping a SATA HDD for an SSD was a while back, but it is generally snappier and seeing as that price is comparable to a 512GB SATA SSD of similar quality...
As for water cooling: I have
this in two separate PCs. Easy to fit and very effective. I put one in my main Plex and backup PC which runs 24x7. It uses an elderly i7 860 in a relatively small case along with 6 drives. There isn't room for a big air cooler and it was idling around 50C and regularly getting up to 80C. That's within spec but I wasn't comfortable having that in an unattended PC. With the water cooling, it idles around 28C and seldom goes above 40C.
My main desktop was worse. I put a great big Gelid heatsink/fan thing onto its i5 4690K and didn't really think about temperatures which was scary, because I just happened to check when I was doing some video transcoding and found that all the cores were getting within a couple of degrees of 100C. With the Corsair thingy, temperatures now get to about 55C maximum.
The pump and case fan aren't silent, but they're pretty good.