You have 300mb of images on your website? What are all the images for? Do most of your visitors to your website view these images? If so, 3gb a month is WAY too low.
You say you get 400 hits a day (And you're a new site?). Now say each of these visitors views half the images on your website. Thats 150Mb of images. So, 150x400 = 60Gb per day = 1860Gb per month!!!!
Thats only if your visitors view the images. If they don't, then you won't need that much space, dependant on the size of your normal webpages and what images they have on them.
The average webpage is around 50-100k including any images. So if you have 400 visitors a day, thats 620Mb per month if they only view this one webpage. If you have 1000 visitors, then that will be 1.5Gb per month. More than likely, they won't just be visiting this one page, and will view some of your images. This will really add up the bandwidth, so if you really are getting that amount of hits per day, 3Gb is FAR too low.
And for $5 per month, you are looking at 30Mb space, 1-2Gb bandwidth MAX.
For what you are needing, expect to pay around $20 month MINIMUM.
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