Tabular paragraph vertical alignment

It's probably easiest to make the final part part of the main paragraph so it naturally aligns with the last row. Exactly how to do that depends a bit on whether it needs to be multiple line or not, but for example

\documentclass[10pt,a4paper]{report}
\setlength\textwidth{16cm}
\begin{document}
\begin{tabular}{p{2cm}p{10cm}p{2cm}}
10. &
Some text or description here can has more than one line 
Some text or description here can has more than one line 
\hfill 300\hspace{-2cm}\mbox{}\\
\end{tabular}
\end{document}

this looks very much like a toc entry.

i find that it's easier to think of this as a centered (block) paragraph, with the first element sticking out to the left, and the last element sticking out to the right. i also find it's easier to code this as a delimited macro, plain-style. here is a definition that has withstood the test of time.

\documentclass[12pt]{report}
\newdimen{\mylistindent}
\setlength\mylistindent{2cm}
\def\listline #1\\#2\\#3\par{%
  \begingroup
    \rightskip\mylistindent
    \noindent\hangindent\mylistindent
    \hbox to\mylistindent{\ignorespaces #1\hfil}%
    \ignorespaces #2\hfill\rlap{\kern\mylistindent\llap{#3\unskip}}%
    \par
  \endgroup
}

\pagestyle{empty}
\begin{document}

\listline 10\\
   Some text or description here can have more than one line.
   Some text or description here can have more than one line.\\
   200
\par

\noindent Here is some more text that is more than one line to
show that the formatted line stretches out to both margins.

\end{document}