El-co Color in New Jersey is known for its affordable 20x30" poster prints.

https://www.elcocolor.net/index.php/poster-special

I remember one of these had a service that made a 3D relief map (3D print) and then framed it, so you could hang it onto a wall.

For what it's worth, I use Vistaprint. That's not based on an extensive comparison, just that it always works for me and seems comparable in price and quality to other services.

For something DIY, Rasterbator.net can make you a poster-sized print in multiple sheets. You’ll need some elbow grease to assemble the print.

In the US, I've had good results with Staples

A good print on demand that delivers ?

dotphoto.com