When I was a little girl, I used to have a doctor that worked out of his home. I have the fondest memories of getting there early and being able to play with the life-size cardboard blocks. When I saw them in our local craft store, I grabbed one of our 50% off one item coupons (available at least once a month). I was able to grab the 40 piece set for $15 - quite honestly, I would recommend them even if you had to pay more!
The manufacturer recommended age for these blocks are 2 years and up, but my son had a ton of fun of them even when he was a little over a year old. The 40-piece set is made up of 8 large red blocks, 8 medium blue blocks, and 24 small yellow blocks. Because of the way the blocks are assembled, they are extremely tough - more than you might think for cardboard! My son has stood on them quite a few times without anything happening. He did end up chewing the corners on some of them when he was still teething, but they can still be used for building. It's also nice that they are pretty light - when he used to throw things, no damage was done (but time-out was enforced!).
As far as having a toy that lasts awhile - these blocks are tried and true. I would say that my son plays with them at least 4-5 days a week, and sometimes for periods close to an hour. We've learned our primary colors using these blocks, and are making progress with counting/numbers as well. We've built towers to the ceiling, a bowling alley, and all sorts of things!
The only disadvantage to these blocks is that they do take up some space, which may be a concern if you have a small house like ours. I ended up using a rubbermaid bin for storage, and it has worked well. Even though they take up more space than any other toys, I would never think about getting rid of them.
These are one of those simple, relatively inexpensive toys that every kid should have. I would highly recommend them!