To not do this training

[Siennasun]

I've had a terrible time at work this year, which made me sick with stress and caused lots of arguments with DH.

I'm starting a new job soon, less hours, therefore less money and hopefully a lot less stress.

I've also been offered a second job which I could do alongside primary job. It's ad hoc hours and I could accept or decline work as I choose. It's very well paid but sounds quite stressful and tbh I just don't want to do it.
A condition of 2nd job Is attending some training in London. There's no charge for the training but they won't pay expenses so it would cost me quite a bit to attend in travel and accommodation. Also the timing is really inconvenient for various reasons.

I can't defer the training. If I don't attend I will have to decline the second job.

DH and a couple of friends I have talked to in RL think I should do the training, because it's a great opportunity and it's too much money to turn down, etc.

The extra money would be nice but we don't really need it. I don't want to do it. AIBU?

I think I would do it to keep my future options open, but it is a personal decision.

I would do the training.

I've had a do a 180 mile trip for some training this week. No expenses, didn't even get petrol covered. Just the way it is really, if it's worth it to you that is.

How quickly would the extra money from job 2 cover the cost of the training? So how quickly would you be able to recoup the costs?

I costs would be recouped quite quickly if I accept the work, probably in 1-2 days work.
I need to make a decision soon and really don't know what to do

For one to two days' work, I think you ought to do it. You never know how useful it may turn out to be in the longer term.

I would be very tempted to do the training - it's always useful to have an extra skill which attracts higher wages.

While I totally understand why people are saying, "Do it" (and in many ways agree), what I read twice in the op was "I don't want to do it". I think that answers your question.

You don't want to do the training, and you don't want to do the second job. Extra money doesn't make up for extra stress, unless you're on a financial cliff edge, and you're not.

I would do it. In this economy, I don't think it's wise to miss out on an opportunity for training and extra money. But that's me.

Fair enough if you don't want to do the work.
Another option is to do the training - but limit the amount of additional ad-hoc work you choose to do.

If you do the training, would you be pressured in to doing quite a lot of extra hours? Either at work or home. If not? Then it would be a lovely back up to do just now and then - you do seem to need an easier route and shouldn't take on a lot of hours.