How much does fuel cost?

I was reading Ukrainian pilots don’t get enough flying hours because the airforce can’t afford enough fuel. So I was wondering, just how much does the fuel cost, per plane and per pilot per hour, or per year?

Let’s say the backbone of your airforce is 100 fighter jets. And you want to keep your pilots reasonably trained, so that would require at least 100 training hours a year. How much would it cost, and what other measures might you take to reduce costs? Perhaps reducing the number of pilots you have? Is it better to have fewer pilots but have them all be really well trained, or have more pilots but with a lower average of training? Or is it possible to maintain both a lot of pilots, and have them be really well trained, and keep costs low, somehow? Also does the type of training have any effect? For example, 100 hours a year of combat maneuvers is a lot different than 100 hours of simply flying in formation, which should not even be considered training.