GPUs have become very expensive, but if you stay at the high end, selling your current card each time you purchase a new one, you end up spending roughly £600-£800 every 2 years.
Compare this to mobile phones where a lot of people buy the latest phone every year for ~£1000 but phones don't hold their value as well as GPUs, so they're spending £600 yearly for their upgrades... I'd also argue that a yearly phone upgrade is a smaller bump in performance and less of a change than a GPU upgrade. So even though GPUs are expensive, I'd rather shell out for a new GPU than a new phone, and it's not costing as much.