Just saying: If you want to write about DIY mayonnaise this summer, there’s an actual news peg. The price on the commercial kind has suddenly gone caviar-high. We walked into a Gristede’s the other day, and right back out, on seeing Hellmann’s for $6.99 a 30-ounce quart. On sale — the regular price was $8.19. Even using Knoll Krest eggs and Planter’s peanut oil, you could make your own for less. Unfortunately, I pay for the permanence. Even the best homemade mayonnaise has the shelf life of local strawberries.