It's "pre-teen", not "pee-teen", and there's no such word as "costed". We use "cost" for both past and present.
Do people say “ten-something”?
Not in my experience. This brings up another point, though. In my culture, it is common to refer to decades. People speak of the '50s (1950 - 1959) as a period of prosperity and complacency, and the '60s (1960 - 1969) as a time of civil unrest and social change. Some decades even have special epithets, such as the Gay '90s (1890 - 1899; "gay" here is used in the traditional sense, not the modern sense) and the Roaring '20s (1920 - 1929). I'm not sure whether there is any universally accepted terminology to refer to the first two decades of a century. I've heard people call the current decade the "the 2010s", and I suppose that's okay, but these same people tend to refer to the previous decade as "the 2000s", and to me that means the entire century.
He vaguely remembered that it was less than $100 and may be $30, 40, 50 or 60. I was wondering what the expression should be. Maybe the speaker can say that the pen costed a few dozens of dollars or a few ten dollars.
We don't normally speak of dozens of dollars, and "a few ten [anything]" doesn't work. I would stay with "somewhere between thirty and sixty dollars" or "about fifty dollars, give or take ten or so".