I don't use a big come along. Just a nylon strap and ratchet like you would use to tie down a motorcycle or atv to a trailer. It doesn't weigh that much and I always seem to need that extra 5-6 feet to make up for my rope being just a little too short to reach that next tree. And I can use the strap to wrap around the tree if I'm short a tree saver. With 5-6 horses, I often have to run between 3-trees. So two tree savers comes up short.
If I'm trying to cut weight, I just take the pulley. Go by REI and buy a River Rafters emergency pulley or mountain climber pulley. They are machined aluminum and very light. I attach it to the highline with a prussic loop and run the high line thru the rings on the tree saver and back. With the horses moving around and tuggin at night, the prussic loop will slip a little and you will have some slack in the morning. But I'd rather deal with that, than fight to get a frozen knot untied.
The rope I've purchased is not used. It's brand new, I think it's just roll ends that this company sells. The store I frequent has a Rope Room where they sell all kinds of bulk rope. They sell lots of short hanks of what was left over off the rolls. there has been a company out of Idaho that comes down to our Horse Expo each spring and sells a Kevlar Rope that is guaranteed NOT to stretch. It's only a 3/8" diameter, so it's lite and smaller to pack, but has more strength than the heavier ropes. I'll have to see if I can find his website. But since it's Kevlar, it's kinda of expensive. I have lost a few highlines. Since it one of the last things I roll up as we pack camp, I've loaded the horses and driven off and left it in the trees more than once.