I think you had a bargain.
You have probably noticed by now people tend not to give valuations here, they are subjective, prices often vary wildly with fashion let alone the weather. Last year a particular Sklo Union vase was featured in a 'Home' magazine. They had fetched five pounds or less on ebay for the previous couple of years, for a week or two they sold for twenty five pounds or more, then the prices settled back down again. The value is what you can get for it, that depends on too many factors and I have nothing to judge it on apart from what I paid for one recently at a flea market, so not much to go on.
If it was a different size I'd be interested.
Edit: The one I have here (same size) is signed H878 it doesn't have the / and 158 (that's what it looks like), no idea what the extra numbers signify.