The answer to your question is yes, there are good alternatives. First, some observations:

1) As with many bathroom fixtures, there are huge ranges in price and sometimes the variation in quality is minor or even non-existent. I'm sure that Infinity drain is good, but the price is ridiculous. There are excellent choices available from other manufacturers at much better prices.

2) I've rarely found good prices at my local plumbing shops. On my master bath remodel 2 years ago, I wanted to support my local stores, but I could find the same brand names online at anywhere from 20-50% lower (like my American Standard bath tub that was quoted at $3300 locally and that I bought online and got delivered to my house in 3 days for $1620).

3) As linear drains are a relatively new trend, and people aren't quite as familiar with them as traditional drains, it's easy to be persuaded that a high price tag is justified. A linear drain is pretty basic: it has no moving parts and is made of stainless steel. As long as the steel is decent quality, the gauge is decent, and the drain is square and welded up properly there's nothing much else to be concerned about...it's a drain.

4) If you go above 60", it gets pricier because that is a less common size. Be aware that the linear drain should span most of the width of the shower, but it doesn't have to go all the way to the edges. If you had a 60" drain in a 66" wide shower (3" extra on each end), it would be just fine. I went with a 56" wide drain in a 60" shower and it's a non-issue. In addition, since we were re-tiling an existing shower with a central drain, we decided to install the linear drain across the middle of the shower. It still allowed us to use large format tiles and avoided having to relocate the drain:

5) Do not be afraid of buying a linear drain online. If you go with a name brand, or something that gets good reviews on Amazon or Build.com, you should be fine. And you can always return it to those two merchants if you don't like it when you get it.

Okay, enough of my sounding off. When I was looking for a linear drain I researched for quite a while and settled on the Luxe linear drain: it got great reviews everywhere I looked. On arrival I could see that It was built very sturdily, was well-finished, and was totally plumb and true. You can get it several places, but the best price I found for a Luxe was, of all places, Home Depot. You can get a 60" all stainless drain for $259, or the tile insert model for $319: Luxe at Home Depot.

Sixty inches is the standard upper length from most manufacturers, but Luxe also makes custom length drains (at what increase in price I don' t know) if you need something else. Here is their web site: Luxe web site.

Looking at Amazon, they have many linear drains, but few longer than 60". However, I did find this 70" Novalinea drain, with great reviews, for $319: Novalinea 70" drain.

The only caution I would give about buying online is don't go with the bottom of the price barrel. When I was looking, I found several stainless linear drains which were as cheap as $120 for a 60" drain, but I was concerned about the fact that they might have been made of lower quality or lighter gauge stainless, and I wanted something where I was sure about the quality. I'm not familiar with the brands in the link nidnay provided above, but several of them seem to get quite good reviews and were about the same ballpark price as the Luxe. (Pay attention to reviews as a couple of them also had comments about lesser quality or rusting.)

Happy hunting! You should be able to find something you will be completely satisfied with for about $1000 less than you've been quoted.