Expensive - depend on how much you value your time - if you save 10 hours, how much is that worth to you.
A very decent compromise between price and performance is the Ceibo EB-51, it gives you a full ICE (source display, breakpoints etc) only you do not have trace. For some reason it is much cheaper bought from Philips than bought from Ceibo, I paid $400 for mine from a Philips distributor.

As to making your own, the hardware should be fairly simple, a PC loadable RAM as 'ROM' and a bit of logic to disable PSEN to the emulated board together with some logic to keep P0, P2 from acting on ROM access when emulating internal ROM chips. The PC software is another matter, you need to do a lot of stuff, borrow an ICE and have a look.

I do not see how you can make anything even closely resembling an ICE in less than 400 hours, but if your time is worth less than $1, have a go at it.

In either case, have fun

Erik