Barlow lenses and Televue Powermates increase the focal length of the telescope on which they are mounted.
The ratio by which they increase the focal length usually is engraved on the outside of the lens.

I own a similar Vixen HQ 2x Barlow lens.
In January 2005 I bought this Televue 5x Powermate.
I used the - for me -favourable Euro/US$ rate of exchange and bought the Televue 5x Powermate here.
The delivery took 1 week.
Price US$ 168 + shipping to my home the Netherlands US$26 = US$ 194 in total, currently equals to Euro 130
Normal price in Europe: Euro 229 (excl. shipping).
And in March 2006 I bought this Televue 2.5x Powermate.
I used the - for me -favourable Euro/US$ rate of exchange and bought the Televue 2. 5x Powermate here.
The delivery took 10 days.
Price US$ 195 + shipping to my home the Netherlands US$26 = US$ 221 in total, currently equals to Euro 189
The customs charged me an devastating Euro 46, so my expenditure totals to Euro 235.
Lowest normal price in Europe: Euro 229 (excl. shipping), so I just about break even.