Your question is almost impossible to answer.
After defining domainer, then define average.
Then as soon as you find a definition for either of those 2 questions...remember this, things will change often. As you grow, learn and your finances and luck changes, so will your next strategy.
I've been pretty involved in domaining for about 4 years now and I have a ton of time invested in domaining. Each year my strategy was quite a bit different. Each year my results were quite a bit different. 2011 was my best year by far. Finally in my 4th year of domaning I could have actually made this my only income, my livelihood...but luckily I have a pretty great real job so I can afford to make a few mistakes here and there...So I seriously have no idea what an average domainer would be since we are all so different and we each have different measures of success.
Heres a bit of advice though, whatever money you do plan on spending, positively plan on losing your first year. If you actually make money in your first year, you're way ahead of the game.
2nd bit of advice, buy a few great domains rather than a bunch of mediocre domains.
Hmmm, now to define "a few great domains"
That depends on your bankroll. Take the total amount of money you wanted to spend, Cut that amount into thirds, or quarters and buy 3 or 4 domains that you can afford with the amount of money.
Then Market the crap out of them. Marketing works.
Last piece of advice: Take that McDonalds job and read NamePros threads on your breaks.
Good Luck,
Vito