You're better off breeding non- to low-expression pieds to each other. If you outcross to a bloodred from a non-pied line, you would probably not get any pied babies in the first generation. You can possibly get a high-expression pied from low-expression parents- the high amount of white on parents isn't an absolute guarantee of high-expression offspring.
There are a couple different "lines" of pied- you'd have to do more research about if they are compatible or not. I can't remember. One line is McDonald.
It's okay to breed siblings, depending on if their parents and grandparents were also siblings. If they produce defects, then don't breed them together again. In _my_ experience, I have not had genetic problems breeding siblings; but I have had some defects with distantly-related snakes. It's also a good idea to outcross if you can.
It's probably just a fluke that you've found pieds that are cheaper than regular bloodreds. But low-expression pieds run just about the same as "plain" bloodreds, usually. This time of year you'll run into people trying to clear out last year's babies for this year's, out-of-egg sales, and people with the first hatchlings of the year, commanding a higher price. You just have to shop around, but let the reputation of the breeder and the quality of the animal be the deciding factor, rather than who has the cheapest price.