Beer Coaster Artwork Resolution Upgrade

I have a set of beer-coaster designs saved as low-res PNGs and I need them converted into a single, press-ready PDF in high resolution (minimum 300 dpi, CMYK). During the upgrade I’d like a few subtle... (Budget: $30 - $250 AUD, Jobs: Adobe Illustrator, Adobe Photoshop, Graphic Design, Illustrator, Photoshop, Photoshop Design, Print Design, Visual Arts)