Rough cylinder prices are £30 new 3000psi, perfectly adequate
£150 new for fibre 4500psi. With this you should look around and get a feel for the right size/shape cylinder for you ergonomicaly
Second hand ones mostly for for around £80 and fluctuate depending on desirability of the cylinder /'regulator, age and how long to the next test
Other ultralight cylinders etc will cost a bit more new