For cheap boards use scraps from other projects.

If you are out of a particular color paper for matting your photos, then you could use some regular white and a thick marker pen and color your own!

Save some cancelled postage stamps from the envelopes containing birthday cards, wedding cards, graduation cards or baby cards. Fun borders can be made to go with layouts of these events. Use Archival Mist to de-acidify the stamps.

Also save you ticket stubs from different activites or game tickets from place like Chunk E Cheese or the game zone... or prize tickets depending on the lay out

For perfectly straight borders and mats with even sides use a clear quilting ruler, a glass or plastic mat and an "exacto" type knife or pen.

Use the little pictures you get from your photo index when you have your (digital) pictures developed as a border. This lets you include all your photos on one page.