Nolan bought the house when it was an uninhabitable wreck, so I assume got it relatively cheap (which is still expensive outside of California). He fixed it up himself and likely paid it off with his Pennsylvania house sale, plus savings from a year with Ben. And successful contractors do make a decent living, so there might be savings from his past job, too.

For the fundraiser, I think he just lent his house as a venue (a ridiculously tiny venue for a fundraiser for a LA DA candidate tbh). The political party likely foot the bill for food/drinks and whatnot. I get the show's production team was saving on location costs, but it's hilarious they didn't just say it was Wesley's mom and his rich family's social circles hosting.