youre not going to find tights that will bring you in the single digits unless you find it at goodwill or some other second hand store. However, I have done quite well with some non-athletic "wool" type material leggings from Forever21..they were probably no more than $15.
The best bang for your buck will be underarmour frosty tights. they are about 50 but they are worth the investment. If you run everyday, and the weather stays cold, you will most likely be wearing the same tights every day. A quality pair of tights will endure the constant wear.
Another pair that I love are the Sugoi MidZero tights (a subzero tight is also made for even colder temps). These are more comfortable, in my opinion, than the underarmour tights. They were around $70 but DEFINITELY worth the investment for an everyday runner in cold temperatures; i wore them pretty much every day.
Bottom line is don't be a cheapskate when it comes to tights -- you will be thankful when you're kept warm in your high-end tights