Hi Michelle, welcome to the forums
I agree with Lee and Lily - you learned a tough lesson early on with getting burned as a sub. There are clients who may try to do the same thing so be sure to get your contracts in order, require deposits, etc. and treat other VAs with whom you might be working as any other client.
I don't think that all subcontracting situations are at the low end, though that does seem to be the trend. If you're offered rates that don't fulfill your needs as a service provider, then it may be better to pass on the opportunity. If you're busy working with people who don't pay a respectful fee then you're possibly missing out on those who will pay the rates you deserve.
With all that said, what you've experienced makes you a wiser and more prepared business owner so hopefully moving forward you can create more equitable situations.
I'll look forward to chatting with you further on the boards!