Any advise on the lowest cost door seals (including threshold).

I have seen many kits available for $200-$500 depending on 'quality' of seal and durability.

Any lower cost options like plain old neoprene weather stripping any good?

What about low cost options for the threshold.

db

You can buy just a threshold at Home Depot reasonably. You'll likely have to trim the door length for a good fit but it will work. Neoprene seals will certainly help also and are inexpensive. You may have to replace them every few years just like the outside ones.

Bryan

Do you think automatic door seals are unnecessary? Plain-jane weather-stripping would be quite cheap and convenient if it's just as good as expensive automatic door seals. What do you think?

Dumb question - can you buy a threshold that is high enough to accept carpeting on both sides - I suspect they are only normally designed for carpet on one side due to their normal external use.

Yes, you can buy a threshold that will accept carpeting on both sides. Or, you can make your own if goign the wood route.

As for low cost automatic door seals, I believe that these are only $50-60: http://www.citysoundproofing.com/doorbottoms.html

Also take a look at

http://www.buyweatherstriponline.com/orderinfo.asp?gclid=CMWN18b8sZACFQspFQodDyCxKg

Scroll down the page to the Thresholds section.

Cheers,
Mark