Yeah raising the roof to £150 is doable, but then I might as well go to a parlour. So then, should I just go to a parlour?
I'm at odds with the previous posters on this one - do NOT start compromising on your budget, otherwise you'll be 'finding' that little bit extra every time, and before you know it you'll be shelling out £180 for hour long sessions with premium British wgs (which is the price region most start at).
Your budget of £120 is perfectly fair - but ask yourself what else can you compromise on. Do you need the full hour? Can you pro rata down to 45 mins, or go for a 30 minute option? Travel further afield? The main thing is language - I agree that homegrown talent is always preferable, but ask yourself if it's really worth paying an extra £60 for someone who understands the forward defensive stroke (in cricket, obviously, I'm not referring to a sex thing). You can get excellently reviewed EEs in London still in the £100 per hour range.
Just my two cents - I'm just so terrified of my upper budget suddenly becoming a guide price.