We're getting married at the Hyatt in late October and a good friend of ours is witnessing our ceremony but she has a limited budget and needs a cheap place to stay near our hotel. Please help!!!

Congratulations! I suggest that you check out the Prince Kuhio Condos. We stayed there earlier this month and got a studio condo for $70/night + one time cleaning fee. You can google "gloria's vacation rentals" for the link and scroll down to Poipu and then the Prince Kuhio Condos. The condos are privately owned and they have several under $100/night. We stayed in #214 and it was nice and clean with a pool view (nice pool). It's right on the beach and probably 5 minute drive from the Hyatt.

Waikomo Stream Villas via Grantham Properties or Gloria's Vacation Rentals rent for around $100 a night. Check Grantham's website. You can probably get a gardenview room at the Sheraton for around $200.
-Bill

We stayed at Waikomo Stream Villas room 323 and loved it. It is end unit on second floor. Sitting out on the lanai you overlook the pool and if you have binoculars can see the ocean. Go to: http://www.gloriasvacationrentals.com/#Condominiums....$80-90 per night. Clean and spacious, bedroom, kitchen, living rm, bath with washer and dryer.

Not sure how far from the Hyatt they are, but have often heard Kauai Sands and Best Western Plantation Hale mentioned as reasonable places to stay on Kauai

Those two hotels are in Kapa`a -- 45 minutes or so from Po`ipu.

If the wedding is at the Hyatt, you might want to look for something at that end of the Po`ipu area. I just did a quick search, and found this one -- a B&B on Pe`e Road (close to Hyatt):
http://poipubeach.com/rates.html