Honestly, the Sims 3 doesn't even need a dedicated card. I had a customer buy this laptop, which has integrated intel HD graphics and it ran on FULL settings when she came back to the store looking for a case for it: www.bestbuy.com SKU 1769288, K52f-BIN6 $479.99. I even verified what her definition of FULL settings was to make sure, and yes, truly full settings. This HP for the same price has a better Intel HD card: SKU 2352085, G62-465DX. I myself was surprised, because I always assumed this game required at least some sort of dedicated card, be it a low end one.
Even MicroCenter works if you got a nearby location that has this one: http://www.microcenter.com/single_product_results.phtml?product_id=0360187. Cheaper too.
The AMD Radeon 6450 HD rates only slightly better than an integrated Intel HD graphics. The integrated cards have came a long way from even 2 years ago. So, to look at what you were working with on the slimline, you assumed $280+$110=$390. Yes, it is more than $390 including tax and all that, but your getting a brand new laptop, and if all thats worried about is Sims 3, your all set.
That being said, I wouldn't run Starcraft II on Intel HD. I mean, it'll supposedly work on Low medium settings at decent framerates according to an Intel demo I saw, but if you want High or Ultra settings, you'll need something beefier.