What exactly do you need it for? Time frame? Kind of stone?
A Remorhaz would work. The tunnels it creates should be melted in the sides, which should prevent caveins.
If you have years, the cheapest way is probably to get some kobold miners to work on it. They excavate a number of feet/day equal to their profession: miner check - 10, and three kobold miners can use aid another on the lead miner. So if you hire four level 1 expert kobolds (at 1 sp/day each) for a segment.
The take 10 result would be 10 + 4 (ranks)+2 (racial)+6 (aid another) +2(masterwork pick) +1 (wis)= 25, which is 15' /day. Since "excavation is represented as a fixed number of 5-foot cubes per miner", and you've got four miners there, those four kobolds just tunneled through 60' of solid rock in a day. And all it cost you was 4 sp.
Start two teams of kobolds (each of which contains 12 kobolds, continuously working in 8 hour shifts), one on each end of the tunnel, and have them meet in the middle. It'll take you four months, and cost you almost 400 gp (a quarter of which is going to the masterwork picks, which I assume you'll let the kobolds keep).
Now, the way the price scaling works, you're going to be shelling out 285 gp for the kobold's labor regardless of how long it takes, since 60 kobolds for one day costs the same as one kobold for sixty days.
Now, if you don't want to shell out an additional 50 gp/ 4 kobolds to give the lead miner of each team a masterwork pick, you can go down to reliably excavating 10'/kobold/day. In that case, you'd hire about six hundred kobolds for a week, and have them go at it.
Since each site except the ends can have kobolds going forward and backward, and three shifts of laboring kobolds/day, you'd end up with 600/(3*4*2) +1= 26 different sites (counting the start and end points) where you'd have to begin labor. Difficult, but doable. If you dialed back to a month, you'd need
The moral of the story is that kobolds are industrious little buggers, and wizards ought to know when to subcontract.
And first level characters should be sure as hell those kobolds aren't under contract.