I have to go with a vote to BUY LEGO! Like Nan said, the REPLAY value is a huge argument for buying Lego. 3 summers ago, my kids were getting to a stage where they didn't really play with too many other things besides Yu-Gi-Oh cards (while inside, that is.....outdoors wasn't a problem). So I dug out some of MY old Lego sets that my mom kept and now...our collection has grown to 6 (yes, SIX) BIG rubbermaid, stackable drawers that have been in my living room ever since. I have kids at my house ALL. THE. TIME. and they all play with these little building blocks. You should see some of the creations they come up with.
Ellie, yeah, picking them up isn't fun after you've stepped on a jagged piece, barefooted. But I threaten the kids that any pieces left laying on the floor get sucked up by the vacuum cleaner when it comes thru! LOL
On the subject of PRICE. You can find them on sale every now and again. Toys R Us, without fail, always has a really good sale sometime in October (usually a Buy 2 get 1 free, or something similar). Kohl's is another place that will have them on sale frequently.
Gayle