My son LOVES his erector sets. He's 9 1/2. Two Christmases ago we gave him a giant set, maybe it was two sets, to make numerous different machines - cranes, cars, etc. Through and through he is a builder. LOVES Legos too. He puts all these different sets together to make very interactive machines. This fall he received a set of Snap Circuits and now he has integrated the erector sets with the Snap Circuits and I have motorized things all over my house! I highly recommend the erector set. I will say - it is a zillion little screws and parts that get lost. My suggestion, at least what works for us, is to go to the Dollar Store or 5 Below or something like that and get tiny, plastic containers with lids. He separates all his screws and small pieces into these and then can put all the pieces into a giant storage box without worry that the screws are lost or thrown all over or lost. I remember his set came with a tiny set of tools - sort of non-functional for him as he's so involved. Again, from the Dollar Store or someplace like that he has a small set of tools - screwdrivers of varying sizes, little wrench, etc. It was just a little more functional for him. PERFECT!!
As for pricing, I didn't get any this year (I upgraded his Snap Circuits instead for a larger set) but I know I got his sets at Toys R Us. It was a Black Friday deal so I know it was a decent price. Like Legos, I believe these are pricey sets but also like Legos. I think they are worth it and have stood the test of time with him.
Enjoy!!