Printing my own posters instead of buying...?

A print shop or office supply shop with printing service can do that, BUT you CANNOT take an image from the Internet and get that printed as a poster. (1) It's copyright violation. You didn't take/make the image, someone else did. You do not have permission to reproduce that image, and all print shops, copy services, office stores will refuse to print such an image. (2) Even if you could find a place to do this for you, the quality would suck, because images from the Internet are low resolution. They are not intended for printing.

Sure- you can ask them to blow it up to the size you want, and make sure they do it on good quality paper - No one will know the difference, if it's really good quality. Pricing will depend on the size probably. Call superfine printing-212-827-0063 they do an exceptional job -very good quality color and paper- I get my brochures and flyers there but I don't know about posters. Ask them, they're pretty helpful! Hope it works out!