The training costs with flying are unfortunately high, though the Aer Lingus programme is worth going for when it opens, though it's extremely competitive. The alternative options include waiting for any other sponsored training programme to open up, going down the military route (and planning on staying there for a long time) or self-funding. The latter will require a well-paying job for many years, or funding from family etc.
I'm not going to name my currently employer (who I trained with) on here for privacy reasons, I'll go as far as saying it's a commuter railway in the UK. Difficulty-wise, I'd say the training isn't easy, I didn't find it impossibly hard, it's a combination of hard slog during the theory, then achieving safe and predictable consistency whilst out driving under the supervision of an instructor. Getting in is not easy, the odds are similar to airline cadet programmes and 90%-ish of candidates fail the aptitude tests which are industry-wide. All companies will demand that you live within a certain distance of the depot you've applied for at the time of application, others will allow you to relocate.
The salaries for each individual train company can be found on the ASLEF trade union website. Pay during training is typically about 50% of qualified, sometimes higher. It may increase slightly once you've completed the first 10 weeks or so.
There is a UK railway forum (in some ways similar to PPRuNe) which covers the recruitment and training process in immense detail.
A lot of the people who considered aviation as a career seem to have put the dream behind them once they joined the railway in the UK, they tend to fly as PPLs. The reasons vary but the desire to settle down seems to be a common theme. I did, however, hear of one fellow who drove for SBB in Switzerland for a few years before moving onto SWISS as a pilot.