vBSEO can be hoggish, but as it was suggested here already, using a caching option helps a lot.

I use vBseo before then never get high cpu on my server ( 4core cpu, with ram 4GB : dedicated server )
Try using caching , xcache, apc + nginx proxy :)
I use it, and never got high cpu.
But now I had sold my license because not support multiple domain, then need license per each :)
That's my experience

What are the specs of your semi dedicated? Which host?

How much are you looking to spend? Which country? Managed or Unmanaged? I can get you a dedi for a good price.

its pretty simple....they don't have a solution for fixing the high load so they don't acknowledge it