I did the same job spring of '04 on my '90 3.0. You can see what the local shops will charge to port them, but larger valve package that some offer don't seem to be worth it. The headers will be far easier to install with the heads off, that is how I did mine(using Downey headers). If you run headers you need to install a 1-2" body lift not much clearance on the passenge side firewall, about 1/2", or you can beat the p-side fire wall in with a hammer to give you more clearance if you want to avoid the BL.
My cost was about 1893.39, here is a break down of my cost
Parts
$343.72 Headers
$170.59 Downey X-0ver
$540.63 Complete 2 Head rebuild/new parts/valve adjustment
$215.00 Gasket set
$262.08 Knock sensor & wire/O2 Sensor/T-belt
$ 88.49 Summit Racing heat shielding/misc.
$ 37.41Toyota Dealer/misc.
$210.00 Injectors cleaned and rebuilt
$20.00 Raptor Turbo muffler from Kragen's
$ 5.47 T-belt spring
You can also figure about another $80-100 for water pump, and you can have the injectors cleaned for about $11 a piece, if the O2 is fine you can save yourself some $ there. What ever you do, do not be cheap on the knock sensor and wire, if you don't replace them they fail within about a month after rebuilding everything, every Toy tech and mechanic I talked to said replace them so I did. There are a few here that didn't replace them and the check engine light came on not long after the rebuild. Since the sensor sits between the two heads, the only way to get at it is to tear it down to the heads. I would weld on flanges to the headers so they bolt up rather than slip on, better seal IMO.
To keep things neat while tearing it down I used cardbord to hold bolts, took plenty of pictures and video to use on the rebuild, came in handy and made the rebuild a piece of cake. Also download the FSM at the head of this forum, I only had the use of a chilton's and haynes, the FSM is a lot clearer.
