Like I promised I will now reveal how I managed to keep my hair red for 8 months without having to dye it every couple of weeks.
I used Manic Panic Vampire Red Amplified to get this dark, deep red. Before dying your hair, make sure it's healthy. Manic Panic has to be applied on wet, washed hair. It is very important that you do not use conditioner right before you are going to dye it. I dyed my hair from a very dark brown to vampire red without using bleach. If your hair is lighter or you bleach it, it might turn out brighter!
My mother always dyes my hair, using gloves and a brush (you have to buy these separate since it's not included in the box) For my hair, I have a lot of hair, just over shoulder length, one bottle is enough. The instructions say: how longer you leave the dye in your hair, how brighter the colour will be. They advise to rinse your hair after half an hour. I, however, left it on a whole night. I slept with it. How? Well I gathered all my hair and put in a plastic bag that I used like some kind of hat. It looks incredibly silly and it's not comfortable, but it works. Be sure to put an old towel on your pillow or use an old pillow case because the bag might loosen a bit during the night. In the morning you rinse your hair (not until the water is clear, but until you think most of the dye is out of it) and you apply conditioner.
Be careful with towels and clothes. Your hair will stain the towels and can stain your clothes if your hair gets wet (sweating, rain). It's been more than two months since I last dyed my hair in this way, and my shower/bath water still colours red. This is perfectly normal. This means, however, it can still stain clothes and towels! I do not use any special type of shampoo or conditioner to keep my hair red, but some people advise moisturising shampoo and conditioner. The only thing I do is wash my hair as little as possible. If you can't bear that, use dry-shampoo.
Dying your hair red doesn't have to be expensive or high maintenance, you just have to know how. Be careful if you want to keep another dye than Manic Panic in your hair for the whole night since it might damage your hair. Manic Panic does not damage your hair by keeping it on very long.