So, there a couple of basics to get out of the way first.

1. Pentax DSLRs are just fine compared to Canon and Nikon; they're solidly built, have a decent but smaller following, and in fact often have better features at the same price level (because they need to, to compete). That's not to say blindly that "Pentax Is The Best!"; in fact, they're all great and I wouldn't worry too much about tales of woe. Canon and Nikon do dominate the market, and for some people that's a factor (either a pro or a con, depending on personality!)

2. You'll have to manually-focus these old lenses on any camera, as they predate autofocus.

3. Sadly, none of these lenses are very exciting. Pentax has made a number of great 50mm lenses over the years, but the 50mm f/2 is not one of them. The 35mm f/3.5 is generally well-regarded for what it is (it's very sharp) — and in fact might be fine for starting landscape work — but it's also quite slow (at maximum aperture of f/3.5). I don't think any of the bunch here is worth over $50.

So, #3 is kind of a key here. If you get a Pentax camera, you'll be able to use these, and that can be fun and useful and interesting, but you'll also want some better lenses. Don't base your decision on that. Instead, take a look at:

• What should I look for when shopping for my first DSLR?
• What are considerations when choosing a DSLR brand?
• How much do lens lineups vary across DSLR platforms?
• How can a telephoto lens take great landscape photos?
• What fixed lens to use on a cropped sensor DSLR for mountain landscape photography?

...and others, and don't hesitate to ask new questions to help clarify your understanding.

Going back to the basics to conclude, though:

• This is kind of an expensive hobby. As you get more into it, you'll find that you'll want to spend quite a bit more on lenses than you do on a camera body. Although the various different brands are all excellent and at one level it doesn't matter too much which one you commit to, it can be a commitment. Rather than worrying about initial savings, look at the bigger picture. On the other hand, the even bigger picture isn that it's less important to worry about all of this than to get something that will get you out taking photographs. Once you've spent some time doing, you'll have a feel for what is holding you back. For now, basically anything decent will do, and just about anything you choose will give you plenty of room to grow.