My house had a full basement but was built on in the mid 70's (the addition has a crawlspace). I saw 3 termite mud tunnels running up the block foundation in my crawlspace (but no obvious damage to surrounding wood) and so I called Terminex for a free estimate. They said they'd either inject the perimeter of the footing with fipronil and drill the concrete front porch and inject lots of fipronil there or set out poison bait stations around the perimeter- 10 year guarantee- for $2K.
I bought the fipronil concentrate off amazon, spend a half day digging a trench around the foundation and drilling the front porch in several places, then injected the fipronil myself with a 30 psi sprayer pump/wand (the pressure of the chemical spraying would "drill" down deeper- so I could get the sprayer tip underground at least 10")- total cost to me was about $75. I knocked down the mud tunnels and soaked that area good- that was last year and so far, no more tunnels.
I asked if the terminex rep if for the $2K they would be drilling lots of holes through the sill in the crawlspace so they could inject chemical down into every void in the concrete blocks- and his response was "no- we don't do that anymore- it isn't necessary".