There are three costs to entering the market. The first cost is the gold cost of levelling. The second cost is time – and you need lots of it, to get all the glyphs it will likely take 2 to 3 months of daily cool down research. The third cost is the gold cost of stocking up initially.
To level there are various quick guides out there such as: http://www.wow-professions.com/wowguides/wow-inscription-guide.htmland http://www.elsprofessions.com/inscription/tells all there is to know about the inscription profession generally.
If there are sufficient herbs and inks on the AH, you can do the first part of the levelling in one sitting.
In order to learn all of the glyphs you will have to conduct both Northrend Inscription Research for 42 glyphs and Minor Inscription dailies for 64 glyphs. In all, this will take you about 54 days if you got the timing right, most likely 2 to 3 months though.
In addition there are c54 glyphs that can only be learned from Books of Glyph Mastery – with the coming of Cataclysm there are fewer and fewer of these books to be found on the Auction House as they are WotLK world drops - many times they will sell for 500g+ each - by no means a small price to pay to learn a recipe.
As an aside, if you have surplus Books of Glyph Mastery keep back a couple and flip the rest. You never know when a new glyphs will arrive that will require the book.