There are numerous discounts, but there is a ticket on-line calculator called "jizdenka", www.jizdenka.cz.
Accordning it, the regular, non-discounted couch price is 63.40 Euro - which is a freaking expensive for that trip. Don't forget, even a regular Breclav-Warszawa ticket is a mere 34.20 Euro, but it could be done for even less.
Best of all: Budapest-Warszawa (essentially the same train, it is joined by Vienna-Warszawa in Breclav) is a mere 29 Euro. It's a special price, but there is no on-line reservation, so that special won't be sold out on-line.
So essentially it is cheaper to go to Budapest first, buy the 29 special (it's rarely sold out, even to Praha!), the sleeper is cheaper, too.
Finally: don't forget, the train tariff in Europe is very assymetrical: same trip starting from "East" is usually MUCH cheaper.
In other words: fly to Budapest, buy one round-trip to Vienna (29 Euro the round-trip) and after returning, buy 29 Euro special to Warszawa.
The cheapest city in Europe to fly into (and from the States you get a free day in London) is Belgrade, fly with Virgin Atlantic, change to JAT in London. We did the same for years and saved a lot. The entire airplane ticket is issued by JAT consolidators and it beats anything you can get on-line. Our source of the tickets was mishatours, www.mishatours.com, (800) 272-5811,
Once in BEG, keep in mind, the one-way ticket to Budapest is 15 Euro, r/t is 26 Euro. Buy the ticket to Warszawa or Vienna in Budapest.
It's much easier than you think and keep in mind two things:
1) The average salary (income is more!) in some Central European countries is in the range of $500/month - before the tax. People still travel. That means, the tickets are cheaper than you expect.
2) many people don't have internet, so it's not being sold on-line.
Forget buying anything related to European rail travel in the States. It will be a major rip-off. For regular, non-discounted prices make yourself familiar with www.jizdenka.cz (switch to English!). It is very powerful, but you need to know the train routing to get the exact price, sometimes even so-called "multipliers".
Here is a good FREE map, one of the most useable I know:
http://www.bueker.net/trainspotting/maps.php