Some of the bunker liner firms require their "certified installers" to place the liner. There was also a time when they might have come up to do a few bunkers as a test gratis to help sell. The big boys (last year at least) now want some sort of fee to install a bunker product as a test. However, there are at least 15 bunker liner products out there, and they may all vary in their reaction to a test project, with lesser known products perhaps being more pliable.
When you start the project, it is also tough to get the major players out for just a few bunkers. You probably need to do about half the bunkers on your course as a minimum (i.e. front nine/back nine of grees/fw bunkers if even). Of course, your experience may vary.
Also, based on my experience through late last year, installing new bunker liner, re-sand, etc. probably cost $8-10 per SF. Shaping into new shapes requires a dozer and shaper, and will add tens of thousands to project cost. While sorely needed at most courses, I have found that too many clubs opt only to add liner back to existing bunkers to save money, rather than spend whatever it takes to make the bunkers better for play and aesthetics. Hiring a gca is also critical to best results, but may also cost thousands to tens of thousands (whether hidden in the shaping fee or as an independent consultant) and is often overlooked. On my last project, I offered to develop plans for an old client under $10K and was told I was the low quote by a considerable amount for architectural services! It's busy out there and there seems to be a wide range of fees (and profit margins for contractors) at the moment.
Obviously, I recommend the latter two options in some form, despite the cost. If you are going to fix the bunker problem, go ahead and fix all of it rather than chintz out. The cost divided over the 15-20 year lifespan of the bunker is nominal, especially if considering low interest rate financing.