I could see the cost/benefit trade-off going that way, after all one of the multi-million dollar tunnel boring machines digging the Chunnel was left entombed [1].
That said, I have to wonder if you couldn't use a balloon to extract the digger or even a simple gantry crane over the excavation. A bit of prep before you start digging and you'd save your $15K.
[1] "In December 1990, the French and British TBMs met in the middle and completed the Channel Service Tunnel bore. In all of the tunnels the French TBM was dismantled while the U.K. TBM was turned aside and buried." -- http://www.therobbinscompany.com/en/case-study/the-channel-t...
That said, I have to wonder if you couldn't use a balloon to extract the digger or even a simple gantry crane over the excavation. A bit of prep before you start digging and you'd save your $15K.
[1] "In December 1990, the French and British TBMs met in the middle and completed the Channel Service Tunnel bore. In all of the tunnels the French TBM was dismantled while the U.K. TBM was turned aside and buried." -- http://www.therobbinscompany.com/en/case-study/the-channel-t...