Is Schedule 80 PVC Conduit Suitable for Short Directional Boring?
I don't know what regulations allow, but I have never seen horizontal boring done without installing the HDPE flex conduit as part of the process.

They bore by pushing the bit forward until they hit the destination.  Then they swap the boring bit for a pulling end, and pull the conduit back through the hole as they are removing the drill rod.  There is no separate conduit installation from the boring; you can't realistically push conduit through the bored dirt afterward.

How are you planning on doing the boring?  Is this something you are going to jerry-rig yourself, or hire a company to do?  If you are hiring it out, they likely will have some leftover end spool.  As you say, 30 feet is a small fraction of the 2000ft spool.  It should not be hard to get that as leftovers from the boring company, I would think.

And if you are doing it yourself, perhaps you can still buy some end spool offcuts from a boring company.