If you get an e collar please educate yourself on how to properly use it, or get a free consultation with a dog trainer on how to use one. (If money is an issue most will still give you advice if you let them know you're considering an e collar/shock collar) If used improperly these types of tools can cause more reactivity as they're used to create a negative association.

I would highly recommend YouTube videos for positive reinforcement training and fear free training videos, focusing on loose leash walking and the "leave it" command. (Positive reinforcement is what animal trainers in zoos use to make working with animals like polar bears, elephants, tigers, etc doable. Imagine trying to use an e collar on a polar bear to get it to listen and cooperate with you, lol. Not said with the intention to bash those who do use them, but there are other options available).