Also, no training "pretty much guarantees a job" unless you are on a tagged scheme. This is where the airline preselects candidates prior to training. The Virgin Atlantic and EasyJet MPL schemes are examples of this, as is the BA FPP scheme.
If your son is unable to get onto a tagged scheme, expect to pay another approx £25-30k on top of the advertised training fees. This will pay for a type rating for him, which ought to get him a temporary contract during which time he might impress an airline enough for them to take him on full time.
Finally, and this should have been said first, the first thing you need to do is make sure he can get a Class 1 medical because without this the rest of the questions are moot.