Solutions for big ole ice on the regular?

I'm a water bottle guy.  Usually carry around a 40oz.  My ice usually melts pretty quick.

I've been wandering the interwebs for big molds to fit the bottle opening (2-1/4") and found these:

https://www.amazon.com/TOVOLO-Wide-Mouth-Water-Bottle/dp/B08MXPGNQ8

But they're expensive, and its only two molds, and ideally I'd like most of the capacity in there to be ice (as water is much easier to find than ice) and that would require probably 3-1/2 molds of this size.  No way I'm paying $60 for that.

Anyone have any GRM type solutions?  I thought about PVC pipe, but you probably wouldn't be able to get them out of the pipe.  Silicone molds would probably be the best solution, but I can't think of anything off the shelf that would work.

Just freeze 1/3 a bottle (or more) of water in the bottle and send it. 

What's your water bottle? The Yeti flask I carry around day to day can hold ice overnight if I leave it closed up. Use something with good insulation and a closed top. My wife has found that using a plastic "straw top" on her Yeti tumbler means she loses ice faster than a screw-on lid.

Big chunks of ice will cool down the same amount of water as the same volume of ice cubes, they'll just transfer the heat more slowly.

+1 to better insulation.

Or freeze it in the bottle.

Or just put more ice in it.

That said, if you are determined to DIY this:

1) you could make a silicone mold of the shape you want

2) you could 3d print a mold (how food-grade it is is questionable, however it will just be water at cold temps, so not exactly bacteria breeding ground)

3) you could cut down the length of one side the PVC pipe and tape or clamp it.  Remove/release it after freezing and it should allow the pipe to flex enough to get out the ice

The Walmart oxark trail yeti copies will hold ice overnight for less than $20. 
 

I use RTIC's 1/2 gallon jug when camping. It will keep ice for several days. If I put too much ice in it, I run out of water until the ice melts. 

For large ice chunks, do a search on Amazon for Ice cube molds. This one makes 4-2.2" balls for $6.