If you want the mic on the same table, you're basically not going to get any better noise isolation than a decent shock mount.

Fortunately, with a little ingenuity, a shock mount is not incredibly hard to DIY.
(In the image I used those cheap-ass rubber bands that turn to sticky mush in a matter of days - but you can do a lot better if you find elastic fabric strips for the same purpose.)

Option 2 is to suspend the mic from the ceiling, but that can still conduct sounds from upstairs and quite possibly from your floor (not a huge concern, but possible).

I do not have the 200$ to spare for a first-party arm and shock mount

So get third-party. No shame in that.