wireless specs

What's the difference in range?
I see wireless routers for as little as $19; most of them are $49; and some
are pretty expensive.
I'm happy with my ZyXEL P-330W 802.11g (I think it was less than $50), but I
only use it to access the internet from within my house. I'll be temporarily
working at a different location and I'll be 100' from it, in a workshop in
the backyard. The router will be on the second floor, and can be located in
the attic, if necessary.
Is there a spec that provides a clue about range? If it won't work at that
distance I'll buy a different one to take with me.
My HP laptop has wireless builtin.


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