Perhaps the article was a cleverly paid advertorial, though I didn't see it, Golf Digest doesn't make the swim well to The Netherlands I guess.
I'm not sure if I quality as serious either, is there a higher category? Average over 100 rounds a year and up until recently nearly everything has been sponsored. Yes, cleverly so I might add (pats self on back ever so slightly). Not because I'm any good but because I'm creative and determine what kind of exposure I can provide those companies that have something I'd like to have. Titleist AP2's (about 4 years old now) but done by a custom fitter. Cost 0 but opportunity cost was a couple hours of advice on marketing and expansion. Wedges, driver, bag all fall under this same category. Also have a belt sponsor and a ball sponsor. These as extensive travel mixes well with social media competitions for example. Ball sponsor uses photos I take of the ball + logo on social media contests. Belt similar. I used to receive my clothing also like that. However, I've been slacking a bit and have a clothing sponsor opening now, someone moved on and changed jobs and the new guy didn't like the idea as much. Never had a shoe arrangement so spend about 300 euro/year there I guess. Recently bought two very nice Adidas rain jackets (a brand which I don't love, not being a fan Sergio, Tommy Haas or the old German national team (soccer). However this stuff was great waterproof, stretchable, breathable material and extremely comfortable, not too mention on closeout at 60% off so I've got 2 at the price of less than a third of one of these $600 jobs. Not a yearly thing so acceptable.
Coaching about 600 euro/year at 50 euro/hour and travel, well another story but I have a lot of "air miles" from weekly air travel so many flights are on pts which helps. Still I make up the difference others spend on equipment with travel costs and then some.
I wonder what the average golfer spends on travel? I guess it won't be that much.
For the record I seriously doubt there is anything remotely average golfer about anyone on this site, with exception of perhaps height and weight. The average golfer I suspect is not hanging out on golf forums of any kind.