Oh Seb, what a tough position they've put you in! Even more so as you're paying for it all out of your pocket...
For what it's worth, I had 7 follicles, which gave me 6 embryos. But of course this was a high fertilisation rate, and 4 would have been more likely. I would still have been pleased with 4.
But if they are unable to reach your other ovary, then 4 would be few follicles, esp as not each one will necessarily contain an egg, not each egg could be ripe, etc. But if you stop now, and start another cycle from fresh, won't they have the same issue with your high ovary? Or do they think this will change/move on another cycle?
If you're only ever going to be able to reach one ovary, do they think you could get many more follicles on the "reachable" one by changing the drugs or dose?
I suppose the key question is which is more precious - time or money. If you can afford to go through with EC now, knowing you might not get THAT many eggs, then I would say go for it. But if money is really tight, and they are confident that they could better stimulate the follies next time, then it would probably make more sense to wait.
For what it's worth, having tried so hard to get this far, I wouldn't be able to give up now, and wait another couple of months to try again - I would go ahead with what I've got, even if it's less than we hoped for. But only you and your DH can make that decision!
Best of luck !