Will you need the scanner often, Trevor, or only occasionally? I know when I worked at Kendrick's the production copiers had a very fast scanner (feeder, though glass was available) for up to 12x18 (greyscale or bitmap), and a slower standalone scanner with feeder & flatbed that would do colour (up to 12x18). Save straight to PDF, and pricing was based on time + a small flat fee ($2-5?). Some place like Staples probably has something too, though I suspect you'll have more luck with the smaller print shops, especially if you want it in colour.

Similar to what Adam suggested - we also had a few artists who paint on huge canvases (6'x6' and bigger) that would take photos of their work. Then they'd tweak it in Photoshop to correct some colours so they could make prints for sale.

If you're scanning something like text, playing with the Curves & Levels in Photoshop will help tweak it to get white paper and dark, sharp text (assuming you're not scanning as bitmap!)