G'Day Sarah,
Before you go out spending more money, it sounds like you need to get your finderscope aligned:
Set it up during the daytime and focus the main scope on some identifiable feature a long way away and lock the scope in that position. Then adjust the finderscope until the cross hairs are on the same object as the main scope.
Was it you that has the back/neck problems? If so, you might need to change the type of finderscope you have (say a right angle/laser/red dot finder), or even add a second one, to help you find what you want.
Once you get the finderscope sorted, the next most important thing is learning how to collimate the scope. It needs to be collimated to give you the best views it can.
A moon filter will simply dim the view through the scope to make looking at bright objects like the moon more comfortable, it won't improve the view
.
Al.