Ok,so firstly check with your doc surgery. Now you are on gabapentin, for D related issues, you may be elegible for free prescriptions. If not, they can still give you a form to complete to pay a single fee per annum rather than for each individual prescription. That should make you a saving over the year.
Secondly, re the alpha lipoid acid, I am afraid you usually get what you pay for, with supplements. Now that Amazon and eBay, and every Tom, **** and Harry are selling supplements over the Internet, it is really quite difficult to distinguish the reputable brands from the snake oil merchants. For this reason, I usually only buy Solgar supplements. It is a brand I know and trust. There are others - some better, I am sure, but whatever you buy, don't go for cheap and cheerful, or OTT claims... and check the 'Use by' dates too.
I do usually buy from Amazon, because we don't have a good Healthfood shop nearby, but I am very wary of all of the above.
Hope that helps!