
Honestly... a raw diet.
Source meat from: discount shelves at supermarkets (and often discounted joints can be cut up, leaving a big meaty bone for the dog and some nice meat for the people so economy all round there);
local meat market - get friendly with them and get to know the stall holders and they will knock money off for 'bulk' purchases (not huge quantities just more than the norm for purely human use).
Local butchers will often GIVE away bones for free and many of these do have a decent amount of meat on them.
Veggies: again discounted stuff in supermarkets, local markets and ask veg stall holders if you they could fill a box with bruised veg/fruit/green leafy bits.
Again here youll find theres bits that can be picked out for human use in things like stews and soups, and less tasty bits can be blended and frozen for the dog. (and for the cat wrt the meat part!).
Supplement this with offal if thats on offer wherever she shops, with the odd raw egg or live yoghurt, or tin of pilchards.
It IS more work than feeding a complete diet out of a bag, but as long as shes willing to trundle round the markets and supermarkets there are bargains to be had for both dogs and people.
The benefits also of cutting out ALL the grain from the dogs diet is HIGHLY likely to be that the allergic symptoms go away.
Grain based foods are one of the top causes of allergic reactions and sadly the cheaper the food the more grain it contains.
By doing a raw diet, shes NOT paying for the packaging, the processing, the advertising or the convenience of dipping a cup into a bag and tipping that into a bowl, more work for her (not much tbh i raw feed FIVE dogs and we live on a very basic wage here!)... but a better diet.
It may not work out as cheap as gusto mind you.. (it might actually if shes good at getting freebies out of people), but there is a very high change it will cut down on this dogs health problems and thus on vetbills, very cheap dog food is often not the cost effective option at all!
As a very very rough guideline, bearing in mind i buy all my dogs food as I am too busy/idle (depending on teh situation) to source things for free .... my five dogs which are.... saluki x, deerhound, staffy x, bedlington terrier x and tibetan terrier... cost me under £100 a month to feed.
Sounds a lot, but worked out very basically per dog thats £20 per dog per month, or £5 per dog per week.
I also have dogs who are allergic to grains/cereals... no interdigital cysts here (we did have them when on complete food) or any other symptoms!
Cannot promise that a raw diet will prevent the problem, there is always the chance the dog could be allergic to something else, but it is very very definately worth trying, it may well solve the problem!