Carlson, Vitamin D, 2000 IU, 360 Soft Gels are an excellent product and I wouldn't want to put anyone off using them but I use D3 (5,000IU) 250ct details and I find these are both effective and cheap. Maybe it's because I always take my powder filled vitamin d capsule with my breakfast so there is always food available to stimulate the digestive system.
~~~~~~ earns you a $5 Iherb discount if you haven't used them before.
Vitalady.com may be a tad cheaper for the biotech vit d powder form as they sell an own brand version that's made by Biotech.

UK readers with fibro must take not of the fact that those USA posters using 4000iu/daily do have the advantage of living nearer the Equator (more days of UVB annually) on a continent (more hours sunshine daily than our cloud covered island) and where Vit d fortified milk/cereals are readily available.
It would be equivalent for a UK reader to use 5000iu as a daily base level amount as that will ensure your basic daily bodily need for Vit d is met and your sun exposure obtained vit d can be stored as necessary. Amounts up to 10,000iu/daily are absolutely risk free.