Lampard16, aligning the decimals along a vertical axis using a tabulator, as mentioned by utnik, is the proper way to get the decimal points lined up (similar to how word processors do it).
(One other quick and nasty method would be to use one text frame for the descriptions and one for the figures. You can then make the font for the figures a non-proportional one and then right-justify the whole frame. Like I said, it's nasty, but it works if you want something very simple.)
However, after reading your post more carefully - where your decimal points don't line up in your example and you say you want to "line the description and the price up" - it seems to me that you have your descriptions in one frame and your prices in another and are trying to make sure that each matching description and price is at the same vertical position so that they both "line up" along a horizontal.
If this is what you want to do then you should use the baseline grid. This wiki page describes the basics:
http://wiki.scribus.net/canvas/Working_with_text_frames and a search in the Scribus Manual (if you have access) for "baseline" will show a good description in the "Working with Text" section.
My apologies if I've misunderstood your requirements.