hi rx
the color drawing was for folks who may be aware of VISIO but not think it's powerful enough. i know you were more interested in the railing drawing.
VISIO 2013 is on amazon for $300 but you can get earlier versions cheaper. i still use 2003 for my work.
VISIO allows you to easily draw lines and give them thicknesses to 3 decimal points which is what you need. you can also get very specific on placement. it supports all the export files.
it is much easier to learn than a CAD program and gives you more options for colors (though not to the extent of the pricier ADOBE ILLUSTRATOR). there are tons of books out there to learn it too.
i have not used any of the less expensive CAD programs so can't comment on them.
another consideration is open source free drawing software just to get an idea about different types of drawing programs.