The blowers are configured differently for their mounting location. Also, the external blower has its own cap and damper, whereas the internal blower configuration requires these be provided at additional cost. You could get the fan curves from Wolf if you want to compare performance vs. pressure loss.

You can go straight out the wall from the hood volume so long as the hood is configured for that option.

There are many sources of hoods. Hoods having the quality of the Wolf hood will probably have commensurate pricing. However, not owning any besides a Wolf hood, I cannot comment on specific manufacturers' quality vs. price.

You might check Modernaire for pricing if you can specify just what you want them to build for you. Read the many hood threads here to gain insight into what you need to consider.