You need a PC anyway the price differential is nearly exactly the price of the GPU over the useful life of the GPU given that most users keep their hardware for about 6 years its 700 to buy once, 1200-1400 if you intend to buy the next best thing in 4 years and potentially sell the old one, or 2160 to rent something that can play a tiny fraction of the total games if they don't decide to take it away because its not economical at a moments notice.
If you game 10 hours a week the difference in power usage is probably about $30 a year kind of a rounding error.
Yeah but you need to have a desktop PC to start with. And also don’t forget to add the energy prices.