Any of the Plissoft from Italian Barber are good. I also like the two band tuxedo knot from Stirling soaps. Its my favorite.
Sally beauty supply has the Burbury synthetic under 8 bucks. Buy one get one half off. I will be trying one out tomorrow. Suppose to be a good brush.
I love my Omega S-Brush. It is a tad floppy, but it's easy to load and makes a wonderful lather will all the soaps, creams and gels I use !!!
I agree with Stirling Lil Brudder. I also have the Omega S Brush which is also nice but prefer the Stirling brush.
This is a little oblique to your question, but I think it is still applicable; I started with the $10 genuine badger from Amazon. I recently changed to a $30 synthetic whipped dog. Wow, what a difference. I wish that I had known about those $2 synthetics when I started! How can you go wrong? Still though, I absolutely love the whipped dog synthetic!
My first synthetic was not the cheapest, but it certainly fun. I found an old brush that I liked and restored it with a Maggard's knot.