This is a great meal to share with friends. Pork spare ribs used to be a frugal option but now they're a bit trendy so they've gone from $7-8 a kg to a standard $14kg. (I guess they are the pork equivalent of the lamb shank). I tend to watch the sales and buy them then for about $10kg. While they taste great you do need quite a few because there's lots of bones.
As part of a BBQ when entertaining you can add other things that are cheaper to bulk it out (burgers, sausages etc). The way I look at it is ribs at somewhere like Hogs Breath or The Hard Rock Cafe are around $30 a person and we all ate for about $20 plus sides so that's still a good deal.
Slow-cooker BBQ ribs
Ribs (I had about 500g pp)
1 bottle generic BBQ sauce
1 cup brown sugar
1. Put frozen ribs and bottle of sauce and 1/2 cup brown in slow-cooker. I did 3.5 hours on high but 8 hours on slow works too.
2. Remove ribs and pour sauce into saucepan/skillet, add 1/2 cup of brown sugar. Whisk to combine and reduce by half.
3. Then put ribs on the BBQ and cook basting with sauce till browned.