Paul, getting a new 7 spd freewheel isn't hard to do. I buy the removal key along with the new freewheel. The trick is to find someone that has a removal tool that will remove the old freewheel. Try and see if your local shop will have one, if not, I might have one that will work for ya. Get me a pic of the freewheel without the axle.
https://www.amazon.com/SHIMANO-Tourney-7Spd-14-28T-Freewheel/dp/B003B8JYPU/ref=sr_1_5?ie=UTF8&qid=1538612940&sr=8-5&keywords=shimano+7-speed+freewheel