Amazon has a Magformers 62 piece set on sale for $63.99 right now. Zulily had some come up at a discount yesterday (they had some come up last week also which is when I bought some). Some of the sets were sold out, but I just checked and they still have the 62 piece set for $63.99 also. (The 62 piece set is currently on sale for $84.99 at Toys R Us).
Zulily had the 14 piece set on sale for $16.99, but it is sold out except for in pastel colors which your boys probably would not appreciate.
If you want to go all out, Zulily has the 144 piece smart set on sale for $172.99. It is $200 at both Target and Amazon right now.
Amazon actually has several different sets that look like they are on a pretty good sale right now if you want to browse.
I've been on the lookout as DD, 8, loves them and they are ridiculously expensive! They play with them at GT game club and GT class at school and they are high on her list. She specified at the store when she showed them to me that for her, it had to be magformers, not magnatiles, but I think that is probably because it is magformers she is playing with at school, not anything against magnatiles. I know there are cheaper tiles out there called Picasso tiles, but I have heard from someone who has both sets that the magnets in the Picasso tiles are not as strong and the structures fall over or apart easier than the Magnatiles. I have no personal knowledge about that though.