You can certainly print them on your home printer if it will print high quality images and accommodate the size paper you need. Otherwise, for prints 11x14" or smaller, I recommend printing at an office supply store. I had mine printed on 110lb white card stock at Office Depot and was very pleased with the results. This is the most cost efficient way I've found to have these printed.

Make sure they are going to print at the correct size (in terms of inches) when you place your order. Once printed, simply trim them to fit. I had mine printed on Ledger (11x17") card stock, then simply trimmed 1.5" off both the top and bottom to fit my 11x14" frames.

For prints 16x20" or larger, you can still use an office supply store, but you will most likely be charged for a poster. I've heard good things about shortrunposters.com (but haven't tried them). Otherwise, Walgreens, Costco, or any place that does large prints will work. Make sure you search online for a coupon!

For a while the money-saving trend was to have 16x20s printed on blueprint paper at places like Staples, but in recent years those stores have caught on and will not print these types of images at such a large size without charging you for a poster. It may vary by location, however, so it's worth checking, as it will save you money.