it really depends on what you are getting engineered as to how much they will charge you.
for instance. a quick ring around from the list i recieved from the dpi after handing in a 'modification approval document', the going rate for a gze into ke70 conversion was around the 1500 dollar mark for a certificate saying it was all legit. thats not to factor in all the parts needed and what not to make it legit in the first place.
i managed to get a guy to do it on the list for little over 1000 dollars.
if ur serious send me a pm and i will pass on his details.
but i suggest as mentioned above, that u notify the dpi of ur intent first, cos there might be a way around getting it engineered if u can.
and make sure u do get the modification approval document in asap, cos they take ages to approve it.
mine took 4 weeks.
goodluck