I'll echo exactly what Turtle Mommy said, don't skimp on the liner. Look for an EPDM rubber liner, and use a quality underlayment. Also, beware when shopping on Amazon and read through the reviews of products offered there. Some of the liners sold by sketchy vendors are pieced together 'scraps' that can fail and leak. Try to shop locally, and/or look to reputable and experienced pond suppliers.
You may be able to find deals on liners on Craigslist and the like...where people purchased supplies then gave up on their project. Just be sure that the items are clean and had been stored in a way that didn't cause damage to them.
1000 gallons is a good effort, and anything worth doing is worth doing right. Buying quality to start with will save you time, headaches, money and effort in the long run.
Best of luck with your project!