5th and 6th gen are pretty ancient.
An i3-12100 motherboard bundle is about £160, will idle with dual NVMes about 20w, and will absolutely slay a similar 5th or 6th gen low power build.
Here is a low power 6th gen intel build. https://mattgadient.com/building-a-low-power-pc-on-skylake-10-watts-idle/
Idle draw is 10w. Total pegged draw is 50w.
They mention an i7-6700t has lower TDP (35w), so that power draw under load would be probably 25-30w.
Which is still 2x higher at idle, and 5x higher under load than a raspberry pi.
Chances are the i7 would run closer to idle when tasked with work that would be stressing the pi, considering it is twice the clock speed and twice the thread count. So, maybe 2x more draw on average (6w vs 15w)?
As for costs, im seeing i7-6700t selling used for £60, new DDR4 is probably another £40, and a new cheap motherboard is £60. A quick ebay search shows refurbbed " i5 6th gens" (no model number) with 8gb of ram and 256gb ssd going for £140 (16gb of ram is £5 more, but for the sake of comparison).
I can buy a 8gb pi4 starter kit for £104 (psu, case, sd card, hdmi cable & pi4 8gb).
Which is cheaper than a refurbished i5 6th gen, and is lower power.
If i was running virtualisation, i would absolutely pay more for something i can eventually stuff 64gb (or more) ram into, as well as multigig/10gb networking.
But for running some home services in a docker compose stack? A pi4 is going to be cheaper in the short and long term.