Will pay for itself many times over. My biggest tip is to set your keywords to 'exact match'. Have them on 'broad match' and you will lose a lot of money. If you imagine the customer will google 'solar panel cleaning telford', have that as an exact match keyword. It will only show when someone types that in. On broad match, if they google 'oven cleaning Shrewsbury' my ad may well show again. They may click it and cost me 60p. But they will only be looking out of curiosity and not because they are serious about having their solar panels cleaned. With Adwords, you don't want curious visitors, that's what organic listings are for. With Adwords, you want the exact buyers to hit your site.
Hope that makes sense and helps!