Trying to work out the true cost of hand quilting thread can be difficult as you can get multipacks along with large spools.
If you want a single spool, then there are several great options under $10, such as the Gutermann Quilting Thread and  Coats & Clark All Purpose Thread.
The SEWING AID All Purpose Polyester Threads are closer to $30, but you get a wide range of spools and a great value for money.
With the AK Trading 4-Pack Navy Blue All Purpose Sewing Thread Cones, you only get one color but that’s on four separate spools with 6000 yards of thread on each. It’s important to not just look at the headline figure but also to work out exactly what you’re getting for your money.