Cost to replace the current inadequate single beam of a fixer-upper in rural Ottawa

I am looking to purchase a serious fixer-upper in rural Ottawa.

I will need to replace the current inadequate single beam structure of the 70+ year old home. The exterior dimensions are 25'w x 18'd, the front runs on the 25' dimension.

Joists run from front to back (18' long). There is an old 6"x 10" beam that was installed near the middle of house perhaps 40 years ago. It does not support the structure correctly as it doesn't actually span the foundation (window located in that section of the wall). Beam is bowing, and is supported by 3 jack posts (poorly) which have however prevented further bowing.

Along the front 25', some nutcase went in and cut out 6 sections of joists (1 for plumbing, 1 for ventilation)...the remaining ones seem damaged from rot, but do not appear to have recent damage. There is 1 jack post holding up the joist where the plumbing is installed. The remaining joist were "attempted to be repaired" (not successfully) by sandwiching 2x10's on one or both sides.

My background is architectural technology...so I am not completely clueless, however I am trying to determine the cost of replacing the main beam (Single or double LVL?) and the 6 joists. Also wondering if instead of the single beam........2 spaced-out beams would be structurally beneficial to securely span on either side of the basement window?

What would the cost to replace the current beam, and to repair (reinforce) the cut-out joists?

Thanks,

Kris