Is the mileage really stored in the meter? I would think it's somewhere else. But I don't really know.
On the extensions..
the stock females are 37$ something, cheaper after locating the brand and number on mouser. It's an IDC housing. Rarer, with a completely different part #, first digits being 82824 not 90980.. usually when searching there will be another non IDC that's cheaper provided you can find the datasheet. toyota female #s, two of 82824-60060 and two of 82824-60050
need 4 of them. There are two different part numbers for all 4 females, they alternate, but they are the same physically, I think it's a color difference. I will post a pic.
One toyota original female 37$. Or sourced from used or an individual or junk yard.
7 aftermarket once found, probably 10$ each
Mating male x 4 also probably 7-11 each. PCB mount I bet with no other options. Finding that takes time also. Data sheet from the female will sometimes list the mate. Also anyone that has the combo meter out can examine the male side. sometimes there's number on the backside face (where the pins come out) in very small same color numbers.
connector
est 140$
Terminals, if every position is filled, 160 at maybe .6 to .25 $
est 30$
Wire is sort of cheap but shipping is not. 8 rolls off 100' 22 awg TXL $5 each plus shipping, 15$. depends on how long you want the adapter/extensions. I keep 9-11 colors of 22 awg but not enough extra to do that part for free.
est 65$ wire
I would think 6 or 7 feet would be long enough to set it on the passenger seat while connected and or driving/not driving. I dislike delcity for wiring because of their shipping cost. But their product is fantastic. IF you figure 6' or 7' extensions, then the remaining 3 or 4 feet can be the Ys for each wire to examine a signal. DDM or scope etc. Adding to it or making them longer from the beginning isn't a big deal either because the cost per foot is cheap once you have it. recommend 4 different colors, one for each plug the Ys should be a different color per 20 position connector.
I wouldn't use cheap wire.
Continuity testing it, making up the wires with Ys and terminals is fairly fast. Still it would take a day make the male female adapters then fit and crimp 160 terminals and solder the Ys in there, 6 hours with beer on the couch. small zip ties or tape. No sheathing, grouped in sets of 20.
shipping
est 50$
They would be of like quality and stand up to repeated connect /disconnect for a long time. The adapter part would look like this pic below minus the extra wires and connector coming off to the left. It goes male -female adapter (black shrink wrap) to female.
total est 300$ and 15$ to ship it to someone.
mapping them all, or all occupied positions for my car would be fairly fast. LX I couldn't do all. nor would the other two previous LC versions.
Most are the same but not all, and there will be less wires in the earlier versions of both models. I will find the wiring schematic for MY 2006. It will take a few days.