Yes but it is not a sli enabled board so you will need the software hack to enable sli. If you don't have two gts 450 then just get a cheap 6850 instead. If you already own one gts 450 and looking to sli to boost things then you should consider that sli hack may not work so it isn't worth the second gts 450 to upgrade.
Can I install 2 ASUS GTS450 graphics card on GIGABYTE
GA-890GPA-UD3H motherboard? I see the MB talks about ATI but nothing about ASUS cards being bridged? Any ideas?
The short answer is no.
The long answer is that as nforce4max said, you COULD try to use a software hack, although I would assume that's beyond your level of comfort. Even if you were comfortable with doing it, it's really hit or miss, and from what I've read/ heard the success rates aren't too high.
Like nforce4max, I would also recommend picking up a newer card instead. I'm guessing you already have one 450, so you could always sell that and upgrade to a 6850. The 6850 is a really nice balance of price/ performance, and I would guess it's right around where your price range is.