Need Treatment Ideas For Dog With Flea Allergy/summer Excema/mange?

Our beautiful 7yr old border collie Jaz has always had a lovely healthy coat. He’d never had fleas until recently when we minded a puppy for a few weeks. It took about a month to get rid of the fleas, then shortly afterwards Jaz’s hair all started falling out and his skin became red and raw in places where he had been scratching. I treated him with homeopathic sulphur which was quite effective and within two weeks he was well on the way to recovery. About 2 weeks ago he went through the same thing again. He still has no fleas so I am thinking he may have become allergic to long grasses on our rural property. However the hom sulphur remedy is working very slowly this time and he is still scratching madly.
I am wondering if anyone has any ideas for treatment – alternative or otherwise. I’m a pensioner and can’t really afford a vet unless I really have to. Any advice would be appreciated!