Is this a dreadful idea?

[GoodBadOrIndifferent]

I'm 35, and until the last 6 months or so had a Caitlin Moran like grey streak, completely natural, looked quite funky.
Now I'm just salt and pepper grey and look old. Tired and old. Is it a dreadful idea to just stick a shop bought colour on? My eyes watered at the price of professional colour, but then I don't spend much on appearence so maybe it's time to start!
Any advice?

If I was going for a radical change of colour, I'd definitely go to a salon - maybe because I've mainly had highlights and I think I'd screw it up I tried to do them at home. If the £££ is too much, can you go to a training salon in your local college - ask the stylists are guided and I used to go for a fraction of the cost and get great results but it does take much longer (only reason I changed, really, don't have time now). I'd go and have a colour/style consultation and they may suggest something completely different you hadn't considered. If you can afford it, seeing as you are feeling you look tired/old then why not treat yourself? If it gives you a boost, worth every penny! Ask if you can have something you can maintain at home or is easy/low maintenance.

Thanks Bingo I'm just worried a shop bought colour would look wierd. Though part of me says that I only spend £150 a year at the hairdressers so why not try a nice colour

If you are in or near London the Vidal Sassoon school is very good. I would check them out.