Not sure how much more it would cost to run. If you only really talk about stuff a pi can do as well, you wont be maxing out your cores. You will use a bit more maybe. Nothing sort of whatever you only really keep in mind for monero mining.
My brother in christ. A used PC has powersupply, case, storage and cooling. This is about the basic kit you need for a proper pi5 experience. You can very easily hit the 100 dollar mark.
Also, most of the used business PC will have 8G RAM, which would put your little ARM funsies up to the $130 budget range.
And you would still only have 4 shitty cores, no expandability.
Not sure how much more it would cost to run. If you only really talk about stuff a pi can do as well, you wont be maxing out your cores. You will use a bit more maybe. Nothing sort of whatever you only really keep in mind for monero mining.