Moving the main panel isn't going to be a cheap proposition. The cheapest would be installing a new (I presume you still want to replace it) tanked heater someplace that gives you the desired panel clearance. That would only be cost a few hundred for the heater and some wire and a small amount of labor.

I'd expect you're talking multiple thousands to relocate the main panel (which means extending all the branch circuits to the new location as well as moving the service and the grounds). It could add up to the most expensive.

If you have gas installed now, I might consider one of the two gas options. I've got a Rinnai tankless in one house and gas tanked in the other. Both are better options in my opinion than a electric tanked unit.

First, tell more about "have been told it's too close to my main panel." Who said so? Did whoever it was elaborate on why the location is now an issue and apparently wasn't when the panel and WH were first installed?

Are you doing this DIY or hiring it out?

Moving the main can turn into a nightmare.

Even if you gut the old panel-board enclosure and use it as a huge junction box, every circuit must be extended.

You can easily run out of room to drill enough holes in joists and studs.

Is the panel on an inside wall and if so what is behind it?

Maybe you can turn it around to the other side. Still a big job.