As we know that naturally human skin generates between 10.000~20,000iu vitamin D3 given full body non burning sun/uvb exposure it is a reasonable assumption that amounts under the level naturally acquired should be within the capacity of our DNA to manage safely.

5000iu ~10,000iu Vitamin D3 supplements are cheaply and easily obtained from the USA.
Grassrootshealth Banner shows most people can attain and maintain a 25(OH)D level around 60ng/ml ~ 150nmol/l with 6000iu/daily D3.

I maintain my 25(OH)D at 64ng/ml with 5000iu/daily + regular full body sun/uvb exposures.

I have put a copy of Vieth's paper
How to Optimize Vitamin D Supplementation to Prevent Cancer, Based on Cellular Adaptation and Hydroxylase Enzymology
online as understanding the importance of keeping a HIGH but STABLE 25(OH)D is extremely important.

One of the main objections to using Ergocalciferol is it's potential for speeding up the catabolism of vitamin D as shown in Vitamin D2 Is Much Less Effective than Vitamin D3 in Humans

Comparison of Daily, Weekly, and Monthly Vitamin D3 in Ethanol Dosing Protocols for Two Months in Elderly Hip Fracture Patients This paper shows that there was little difference in the results of the different regimes however they were only seeking to raise 25(OH)D to 30 ng/ml (75 nmol/liter) and as some people don't achieve optimum bone mineral density until 44ng/ml that is too low a level for safety. Similarly human only store D3 when daily needs for Vitamin D have been met and we only start to have significant D3 reserves when 25(OH)D is above 50ng/ml and Circulating 25-Hydroxyvitamin D Levels in Fully Breastfed Infants on Oral Vitamin D Supplementation shows Vitamin D3 replete human breast milk is only available approaching 60ng/ml, the level human bodies naturally attain and maintain living near naked outdoor lives. (60~80ng/ml)

So if daily supplementation and/or regular sun/uvb exposure isn't practicable the nearest equivalent regime to daily would be weekly usage of 50,000iu.
Fortnightly use of 100,000iu or 200,000iu every 28 days.

Biotech pharmacal supply 50,000iu dry powder filled capsules. If you are buying for your personal use then PHONE your order using one of the cheap prefix call rates (1899 ~ 18185) remembering the time difference and ask for the Wholesale order value to be declared on the outer label. Otherwise you get stung for Tax and £8 Post office handling charge.

For best results these should be taken with the largest meal of the day ideally with butter, or coconut oil. Vitamin D3 is a fat soluble vitamin.

Ideally daily supplement use will keep levels most stable and it's relatively easy to catch up if you miss a day or so.
These are what I use.
Country Life, Vitamin D3, 5,000 IU, 200 Softgels"

I prefer Medium Chain Triglyceride oil as the carrier, it's easily and quickly metabolized and because it encourages fat burning is helpful for weight loss and improved mitochondrial function.

I do not recommend omega 6 oil based vitamin D capsules, There is too much omega in the diet so adding supplemental sources only makes matters worse.
The fish oil based D3 are fine but expensive and the amount of omega 3 they provide is so small as to be insignificant for the extra cost involved.
There are some in olive oil that work out a cheap option but it's not a huge saving and the MCT is far less likely to go rancid as MCT is extremely stable and has a 2 yr shelf life.

I've provided examples from IHERB as their $4 shipping to the UK is cheapest(allow 10 days). $5 discount code WAB666. UK readers keep order value below £18 or pay take + £8 handling charge. USA/Canadian readers may find Amazon/Swanson's/Vitacost etc cheaper depending on local shipping charges.