I have no problem with either of the recommendations you got for the polarizer. Those brands would be fine, I'd ad Heliopan as another top quality one. In these, the multi-coated versions are best.... and shop around for the best price.
I'd try to avoid step rings... They get in the way of lens hoods, which are every bit as important as filters to help your image quality, sometimes more-so. That means you will need both 67mm and 77mm CPLs, if you want one for each lens. If you can't swing both right now, I'd just get the 67mm for the lens more likely to be used for landscapes, if that's where you feel you will most often use this filter.
There are less expensive brands of CPLs, some with multi-coating. The above brands are "the best", but you might get a pretty darned good one that costs a lot less. Try to get multi-coated, or go with one that's single coated or not at all and just be very certain to always shade it with a lens hood.
Do you really need an ND filter? A polarizer can sometimes serve instead, since it cuts over a stop of light. On the other hand, an ND isn't really all that expensive. Again, I'd guess you would mostly need it on your landscape lens. And, a simple, screw-in one is usually the easiest and cheapest route for an ND (but definitely not for a Graduated ND).
By the way, perhaps you are already aware of this... sunrise/sunset - with the sun in or near the image area - is one time when it's a big no-no to put any filter on your lens, especially a polarizer due to it's two layers. In this situation you are almost guaranteed to get a lot of flare, artifacts and lower contrast if you install a filter. It's practically always better to just leave the filter off.
Cokin P-series has two "Gray Graduated" that are ND Grads, might be a less expensive alternative, but I haven't looked at the prices of them lately. Definitely get the P-Series filter holder, but will you use it on the tele zoom at all? You might only really need the ND Grad on the wider lens. Lee is another manufacturer who makes filters and accessories to fit Cokin P-Series.
Cokin also sells a modular, clip on hood for their P filter holder. Might be a good idea. I use a Lee hood for mine, but it's more expensive. I think you would only need a single segment of the hood, for your 17-50 lens.
Have you shopped used? A couple weeks ago I went to a local Photo Fair that's held in my area every few months. There is one seller there who has thousands of filters, all perfectly usable. This is the sort of place I'd look for a screw-in ND filter, for example. There's also a shop in my area that has a lot of used filters all the time. This might be a way to make your budget go a lot farther.
Hope this helps. Enjoy the trip!