New to this, How expensive is this hobby?

[Lyle]

Originally Posted by Lmackattack

Welcome to the site... Figure a base king hauler kit is 350-400 add in 200 for a radio. 150 for electronics. That's if you buy new.

If you search eBay you can get the whole package used for around 500-600

What about things like excavators? And can kits be pre-made or are they generally built from scratch?

[Acadieman]

I'll let others chime in, but from what I gather some people have built bruder conversions from roughly $800 and up. The sky is the limit for how much you want to spend.

There are kits for every level, some come as parts, others pre assembled.
Its best to look at some of the post and to follow for a while to determine what you want.