Looking into putting siding on, it currently has old slate and was built in 1880. Does anyone have an estimated guess on what this will total?

You have 2000 spr/ft of wall space which translates into "20 square". A "square" is a 100 sqr/ft (10 x 10 area). You use the term "square" when it comes to siding and roof shingles.
So you can expect the siding install to be about $250.00 per square. This is a base price for the siding installation and materials only. It may be more or less depending where you live. Also take into consideration this doesn't usually include waste removal, capping the windows, house prepping (slate removal,backer board, etc), soffits or fascia coverings.

Best thing to do is get estimates.