I have not yet got my type IV running (to go into my 63 bug project) so can't comment on personal experience re. performance. However they are reported to have a lot more torque than a comparable type I however will not be able to achieve the same outright HP figures (according to the type4rum on shop talk forums). They will be more reliable due to the case material used and will need less line bores. Not sure about the weight, but probably a bit heavier.
Having almost completed the rebuild, yes they are a little more expensive, especially when you have to convert to upright, as well as new exhaust etc...and bearings are a pain in the arse to find. So far my approx costs for the rebuild are:
2nd hand 2L $250
Machining and balancing $800
Adaptor collar for gearbox to convert to later throwout bearing $50
Headwork (convert to 1800 valves, 3 angle valve grind etc) plus lifter resurface $560
Cam regrind $110
Dual dells (40mm) inc linkage $800
Upright conversion including oil lines $700 approx
Gasket kit $90
Assembly $440
215mm flywheel and clutch/pressure plate $150 I think? can't remember
plus new alternator, dizzy etc stuff you may already have.
So basically it would be cheaper to build a type I but then again you can spend a fortune on them. I didn't have to have head work, or balancing, or lightened flywheel etc etc. You could just bolt in a healthy 2L and away you go - just have to pay for the upright kit and exhaust. Hope this info helps. Definitely check out
www.shoptalkforums.com - type4rum though.
Alan