If you're looking for ESB, it's kind of complicated. RS Propmasters and Machine Craft Repicas make the most accurate lineage ROTJ Special Edition castings, but they're not cheap. You'd have to do a lot of work to convert it back to ESB.
You can buy a Wasted Fugly kit from Viva Fett, which is a cleaned up ESB casting derived from the Machine Craft helmet.
Minutefett is also selling a lineage casting derived from the Machine Craft helmet. He recently started selling an updated version that he touts as the most accurate ESB casting. But the issue of recasting complicates things here. His previous version was on par with the Wasted Fugly, but the lineage of his new helmet seems sketchy to me.
Pretty much everything else out there is fan sculpts.
I think the EFX PCR helmet is the best budget friendly option for a complete ESB helmet. Unfortunately it's plastic instead of fiberglass, but you do get aluminum ears. If you were to commission someone to accurately paint an ESB or ROTJ Fett helmet instead of doing it yourself, you'd be looking at about an additional $500 to $1000 depending on who you ask.