I know it's a problem as I've encountered it too and my altar level is now around 330 so you can guess how many re-rolls it takes to get an extract.
The ONLY way around the problem I've found is to have a high level item (Ilvl 130+) that I use purely for re-rolling to get extracts. Yes there are many rolls I would love to keep, but I deliberately don't look at what it's rolled as.
I then use insignia to roll on for finding new enchants and extract them with the stockpiled extracts from rolling on the high level junk item.