I let my friend dye my hair bleach blonde - and it has gone very bright blonde - some bits nearly white. I'm desperate to get it back to my previous colour, definitely without growing it out and if possible not spending a load of money at the hairdressers.
Is it a bad idea to buy another dye that is close to my natural hair colour (mid blonde) or would that end in disaster? Please help!

Dying your own hair is not a very difficult process there are always instructions on the back of the hair dye kit and it only cost about 10-20 dollars for a hair dye kit, if you have the courage you should try that.You can even dye your hair a color you want!

Your hair could be quite porous just now.
Dying your hair at home could make it somewhat patchy as you said you had some white bits?
Please do go to a stylist and let them take it from there as it could be a bit risky doing at home and ending up with a patchy result.

It's so much easier to go darker than it is to go lighter. However, it's important to choose the right base hair color to prevent unpleasant hues in the hair such as green or gray. The white streaks or spots are caused by leaving the bleach on too long. You will need to use a blonde protein color filler on the over-bleached spots and then apply the desired hair color to achieve an even color. When coloring your hair, choose a warm or neutral base hair color to prevent unpleasant tones in your hair. If possible, get it professionally done.