I have some black liquid rubber Isoflex as above used for fixing settlement cracks on the garage roof some years ago, so effectively free. It is a bit thick though e.g. much thicker as an example than golden syrup and does not taste quite as good, so have to factor in the cost of something to thin it a little.
Tesco among others (via an "Approved Partner" {are they trying to do an Amazon?} ) have liquid latex for £11.95, £15.20 including delivery for 1 L
Being somewhat of an expert on rubber (gloves :-)) the cheaper pairs are A. Worse at breaking and B. Not usually available in large or extra large. (hint... use some form of drying powder like talcum powder or Lanacane powder (expensive but not talcum and very good) inside the gloves to prevent them getting stuck to your hands) as getting them stuck when putting them on and off is probably responsible for tears and pin holes. Asda did their usual, sell the branded make for a while, then substitute their own brand which apart from not available in x-large were of inferior quality too.
One or two web pages on the subject suggest turning the gloves inside out cleaning with alcohol and applying liquid rubber like substances, then the same procedure on the outside.
My time is free (but don't send me your rubber gloves to mend ! but I would accept them as gifts assuming they are not contaminated) as I'm retired.
Statistically the chances of the same glove getting damaged is not likely so in theory buying more pairs and matching unbroken gloves is a possible scenario, but unless bought in bulk it may be difficult to get the same make. Having said that as they are not as fashion accessory then wearing different colours/makes etc. isn't a problem :-))
I suspect paying more for the gloves and using the types (more like rubber gauntlets) intended for handling corrosive chemicals may be a better approach.
Haven't done the sums