Wild guesses.
A heavy matte paper (because nobody in their right minds clips lustre/gloss), printed from the beginning of the roll (because the tail end is so much fun). 64" printer and stock, with a generous overlap on the two printed panels. Trim one, with some overlap remaining, lay over second print and trim with a damned sharp scalpel through both paper for perfect alignment. possibly trim top or bottom border, to get horizontal alignment, or mark T&B on the reverse. If the print has a border, then trim T&B to border.
Filp print and place on the Big Table
Something along the lines of a linen hinging tape down the centre, and possibly around edges.
I'd bill something like this, assuming I had a 64" printer and a 6x10' printer as at least 400% of a 72x60 print, probably much more, as I'd factor in failure rate (400% increase), time and labour (at least 2 people). Unless I'd done this many times before, and had systems in place.
Real cost, the print & time & risk, plus packaging.