Jeggings/leggings aren't made for riding. Even with knee patches, they're far too thin and will wear out faster than a pant that's actually made for riding horses.
I prefer jods over breeches, but will wear both. Fullseats are great if you have a horse who likes to spook sideways at 300 mph. At inopportune times.
I just bought 2 pairs of jods for $5.00 a pair, and the last breeches I bought were on sale for $20.00. If you keep your eyes open, you can certainly find well made riding pants for a lot less than regular retail.