Suggestions on how to proceed - structural repairs

[Brad Garcia]

My first post on BP and also signed an agreement on my first rental property. the purchase is contingent on nothing major arising from the inspections, but one piece that concerns me is the bones of this 1900 home. 

The upper floors shows 1"+ Sagging of the floors, so much as you can really feel the slope walking through the rooms. Figured the beams in the unfinished basement need to be adjusted, but found a maze of beams, some cut into the joists, and a some auxiliary supports. So my concern is, if I mess with one, will it create issues with the other. Also, if it is a hack job, should I have the beams/joists repaired? Everything seems stabilized, but my question is for how long...

I realize that sometimes you just put lipstick on properties, but I feel there is potential in the home if it is sound and will last. 

I am hoping to have a structural engineer to assess my concerns, but is this just my nerves getting to me being my first deal? Has anyone walked away from structural issues or use it to negotiate the price and make the repairs? Also what is the rate for an assessment from a structural engineer?

Thanks!