having been faced with the same conundrum myself recently, I decided to re-build.
A big part of the decision was that there are no re-builders in this part of the country and buying one from down south would be costly on shipping and I wouldn't be able to just nip back to the garage if anything wasn't right.
tbh it was somewhere between a re-fresh and a re-condition rather than a total re-build.
I itemised my costs here-
http://forum.club8090.co.uk/viewtopic.php?f=50&t=159419&start=120 as a guide only, yours could be cheaper if you don't need some of the parts I did and if you live somewhere that's cheaper on postage. equally it may cost you more if you need new pistons and barrels, new con rods, find broken studs or need to get work done by an engineering company.
I did it in 5 weeks, working most evenings and weekends when I wasn't waiting for parts to be delivered.
I didn't swear much during it (except when I drove it off the ramps and onto my front grill that I'd left lying on the ground) and the satisfaction is definitely worth it.
In your position and if you feel your mechanical knowledge is up to it, and you can afford the time necessary, then I'd buy a used engine and re-build it yourselves slow time so you have it when you need it. I lost 5 weeks of the best weather we've had for years as I was stuck in the garage every night.
I also couldn't have done it without the help I had from guys on here, I'm mechanically able and have access to precision measuring equipment but wasn't familiar with the specifics of these engines. I am now. lol.
On the flip side, if you can afford the money to buy a re-built engine you get a guarantee and can get it sorted if it's not fit for use. bearing in mind that some companies may do a re-fresh on the cheap to keep costs down and appear competitive. If you buy are-built one, don't be shy with the cash.
'86 1.9 DG, 4 spd, tintop, camper conversion.
Split case club member.