If you'd like a little land and a break on taxes, your best bet is to look for a place in westerly Linn County (e.g. Halsey, Colorado Lake area) or possibly north Albany area outside of city limits and still keep the commute into Corvallis reasonable. An alternative is looking south of town, but IME when places pop up between Corvallis and Monroe, their previous owners are
really proud of them. 5 acres with a 40 year old single wide? $400k+
Taxes in Corvallis are steep, as you might imagine. They're even steeper in Philomath, just to the west. I bought a house in Corvallis 2ish years ago and really like having the short commute to work in spite of the higher cost of living. Additionally, I've seen my home's value increase in that time. In my particular neighborhood, it isn't uncommon to see newly listed homes go within 24-96 hours after being posted.
Sorry, I don't know a whole lot about local construction firms. I do know that a lot of the construction that is always going on on-campus seems to be done by firms out of Portland and Salem area. Knife River has an aggregate and dirt yard just east of town on highway 34.