You want extreme magnification expect to pay $1800, Canon has a nice 5:1 lens add to that a set of Kenko (about $240) extension rings and you can happily snap a ants head full frame.
More modest you have a choice around $500 for a 1:1 macro lens, Canon, Sigma and Tamron make such. 1:1 means 1 cm on sensor is 1 cm in reality.
If that is still a bit too crazy, go for Kenko extension/macro rings/tubes and a normal lens with decent macro point. I like the Tamron 70-300 (about $190) with 1:2 macro end, but I have not tested in depth.
Next you also want to consider what you want to photograph; insects? The extension rings may not be usefull as they just help to get more close to subject , with some lenses up to 1 mm ! Another point with those rings is they cost light = longer exposure = not suited for flower waving in the wind.
You can also use a magnification front filter. For nature they may work, for objects their fuzzy edge and limited dof may be impossible.
So if you ask me what should I pay, I would say buy the Canon 5:1 lens, please get bored with it and give it to me ;-)