Actually...
If your paper negative is RC, and you have a 4x5 capable enlarger, you can project the negative just as you would a film negative. The image will be dimmer, but exposure times are still quite manageable; with my D2 and Zone VI cold light, I have to stop down to f/22 or f/32 to get manageable times with film, and it wouldn't hurt anything to open up to f/11 to get similar times with an RC negative.
That said, paper negatives tend to be contrasty compared to film, and contrast is controlled by either selecting a different paper (with graded) or a different filter (and the various, potentially bizarre effects of subject color and light color, with VC), and much less so by development (though there are developers that can harden or soften paper contrast by about half a grade compared to the Dektol/D-72 standard). If you look at J&C Photo and Freestyle, you ought to be able to buy ISO 100 film in 4x5 for well under $20 for a box of 25, and Efke 25 is just over $25/25 sheets if you prefer a slower exposure -- and the film you get will fit your film holders without trimming, unlike any size of enlarging paper.
Both sources also have ortho-lith film that runs ISO 6 to 25 and can be handled under red safelight, if you prefer easy inspection development, though I don't recall seeing ortho in 4x5 recently (haven't really been looking, but it's not difficult to recut under safelight); these films may require highly dilute developer to deliver pictorial contrast, but there are plenty of solutions for that problem, including stand development in either HC-110 Dilution G or Rodinal 1:100 (or weaker).
