Apologies for my maybe-stupid question, but where is the challenge? What I mean: it's not like you risk starving or anything.....
My character has digging at double the combat skill, and this is only because at one time I decided to "grind" the combat skills and raised them, otherwise it would be 3x. But it makes no difference: if you stay in a safe area the lack of combat skills is not an handicap to survival, and if you go in dangerous areas chances are you'll be torn apart anyway, 500 HP more won't change the result, the important thing is to learn to avoid aggro, which has nothing to do with combat skills (ok, I'll grant you that extra HP may mean survival in case of source explosion, but that really should not happen).
Locating the spots where to dig is more a matter of tracking sucking horribly at what it should do, but again, if you only want to level digging then WHAT you dig is irrelevant, and finding places for random stuff is not that hard, even without ballistic's map.
You're right on the availability of equipment: I'll try to see if it's possible to dig at 100+ without any focus boost.... hmmm I have 20 mins, I'll try it now
Edit: you can but of course the yield is not as much as it would be with full jewels. After some quick tests, being at digging 140, I can pull out q150 mats without wearing any armor/clothing and without being forced to stop and wait for the source to expire (which means a lot of time wasted). I'm around 3-4 mats short of what I can do with full focus equipment.
Stats: focus 1650
prospection cost: 200 (you have to remove some frills, but I've kept both mat and terrain spec)
For careplan: I used my expensive one: 4+4+mat+terrain
Initial dig: S3G, R4H, Q40G, mat+terrain, execute 3 times (75 focus each)
Execute one careplan
Final dig: S2G, R4H, Q150G, mat+terrain, execute until end of source (112 focus each)
Result 7.8 @ q150.
The dig was done without self-heal after prospecting.
This was done quick without any attempt at optimizing by doing the math, so it's probably possible to do better. It should also be doable to squeeze in one more mat (going to 8) either by extending a bit the source lifetime or by doing a better work with the final dig action (there's enough focus for one more dig at the end).