What is the CHEAPEST way to create some 2x6 raised beds?

Use pallet wood, pallets are free at many companies/businesses:

https://busycreatingmemories.com/diy-pallet-garden/

http://www.penniesintopearls.com/diy-pallet-wood-raised-garden-beds/

http://thecouponproject.com/frugal-gardening-four-inexpensive-raised-bed-ideas/

Walmart carries these, https://www.walmart.ca/en/ip/vegtrug-raised-herb-garden-bed-planter/6000197175493?cmpid=sem_pla_google_en_none_6000197175493_100092103132807_None&cmpid=sem_pla_google_en_none_869128796_44166797216_None&gclid=CjwKCAjwoKDXBRAAEiwA4xnqv_jsRS2mrFHWRyRMrI3EeHWd06vMFIV73Xiinj_OubBoyD4AQJbnzRoCZ4MQAvD_BwE

If you had a bench and a set of old drawers that should work. Just drill holes in the bottom of the drawers, fill with dirt and then plant. Or actually a bench and some pots will also work. That is what this grandmother does with her herbs.

Most raised beds are only about 12 inches tall (or less)... we are in our late 60s and find the galvanized horse trough/stock tanks are perfect for growing vegetables and herbs... you can get the 2 ft tall by 2 ft deep by 4 foot long ones at most places (Tractor Supply, Lowe's, Home Depot, etc) for about $90.

or consider using a metal trash can(s). Put drain holes in the bottom, add good garden soil and plant away. The troughs can be moved if needed (just tip the dirt out onto a tarp). We have grown tomatoes, potatoes, herbs, cucumbers, artichokes, zucchini, carrots, radishes, lettuce and cantaloupe in ours. FYI: melons, cucumbers, etc... can be grown on a trellis to save space and keep the fruit out of the dirt.

If you have any old tires you could stack them and fill with dirt and plant in the top tire. Perhaps filling the bottom with something like styrofoam popcorn until you reach a depth where you can add dirt. You can paint the tires so they look nicer.

I like Debker's answer. I made raised planter beds for myself and they were still too low to the ground. I now have a planter similar to the one she recommended. It is right by my back door and so convenient. Has cooking herbs in it.

2 x 4's or 2 x 8's - check my hometalk projects for ideas.. I have a few raised beds there that are easy to build. Some are 2 x 4 others 2 x 8

Thank you all! Great ideas.. I'm going to get a trough next week, but, for now I took an old bench and anchored some plastic bins to the top. I drilled holes through the plastic and bench for drainage. We have her herb seeds in and today it is raining beautifully. Again, Thank you all!

Get some free pallets and use them for raised garden beds. This would even provide you with the nails. I know of folks who built whole hunting cabins from free pallets. Add the potting or garden soil inside it to make an easy garden for her. How nice of you to do this for her!

Also consider putting pots of the herbs on an old table.