It only takes a few seconds to whizz your flax in the grinder to break the skins so the electric mill doesn't get a huge amount of use so if money is an issue you may find this cheaper one as good. Mains Coffee Bean Spice Pulse Nut Herb Seed Multi Use Grinder £9.99 +£1.20 delivery.
I've been doing this for years now and my cheapo grinder from Aldi or Lidl's (can't remember which) has been fine.

If you can find somewhere that is totally absolutely and completely mouse proof flax seed keeps very well and providing its kept cool and dry should be fine for a couple of years. Mice will chew through that plastic bag and being slippery stuff that gets everywhere it will be all over the floor. Put it in a solid plastic bin with a close fitting lid. Share it with friends and you will all save money.

You may also find your pet food shop is much cheaper than the health food shop. Providing it's clean it should be fine.
Once your ground it then it does degrade quickly so I just grind enough for a week and pop that in the fridge.

Health food stores are a rip off 25 kg brown linseed £54 delivered roughly £1 a 500g compare that with H&B Now: £3.09 Buy 2 for: £4.64 There is absolutely no difference in nutritional content between brown/golden flaxseed so only pay extra if you prefer the colour.

I've just found a local mill who will supply, if I collect, 12.5kg brown whole linseed for £11.10p so that's roughly 50p per 500g.
Doesn't it just make you spit how much these healthfood shops charge for decanting it into a smaller bag.