It all depends on what you want in a character from 1-50.
If you want full set build from level 7 on, it's going to cost you a lot.
If you simply go SOs and up them every level to 50, it's going to cost you a lot.
I'm cheap and I like efficiency, so I stick to lvl 25 IOs at level 22, usually hand-me-downs from other respec'd toons. Also some Quality of Life stuff like KB protection if needed, Perf Shifter Chance for +End, Panacea, Miracle, Numina's, sometimes Preventive Medicine in Health/Heals, Steadfast and Gladiator's, ATO's etc.
Cost?
Somewhere between zero and 50mil, depending on the character, the market, and what's available in storage/mail.