My first year my advertising costs were around 8k. It was the only thing I massively underestimated. I now have very limited advertising but that is still 3k.
As for facebook when it comes to people searching for trades on facebook there are 2 types of people. You have the market place searchers that want cheap and then you have the type that you want and they are the ones that ask their friends by putting up a post on their feed. I'm sure if you spend enough money you can get your advertising through to them as when I was on facebook if I looked at a drill from 1 place the next month I got inundated with advertising of drills but that was always from the big companies like screwfix amazon b&q etc so the ones that spends millions on advertising.
Facebook prides quite good tools for targeted marketing. If your audience is 35-75 year olds living in the north east of England who like jazz music you really can be that specific. You have to pay for the privilege but it wasn’t as much as I’d expected in the past. I’ve found it to be more effective than letter drops in a lot of cases.