Pros of towering:
-Lots of space for expansions of all sorts
-Overheating is no longer a big issue
-The power supply is more than enough for everything on an expanded system
Cons of towering:
-Expensive
-It looses its distinctive appeal as an Amiga, and may be confused by an ordinary PC
-It requires some research on the proper fitting of different expansions. Not all towers allow all expansion combinations
-It nearly always requires lots of adapters for devices like keyboards, floppy drives, PSU, etc.
Bottomline: If you have enough economic resources at hand or you are a very handy DIY guy, go for it.
About costs:
Example one, the "DIY" el cheapo way:
1.Pc tower with PSU - $30
2.PSU adapter - some soldering and patience
3.Modding the backplate for the conectors to match - a metal plate and some cutting and drilling tools
4.Keyboard extension cable mod and new casing for the original A1200 keyboard (I made one with thin wooden panels).
Total $50 plus time, patience and skills
Example two, "My way":
1.Micronik Tower and Amiga adapted PSU (from evilbay)- $100
2.Lyra2 keyboard adapter + PS2 keyboard - $50
3.PCMCIA right angle adapter 35
Total $185 plus shipping costs
Example three, "Elbox way":
1.D-BOX 1200 and PC-key 1200 interface - 240.95
2.PSU 230W A1200 - $46.95
3.Generic PS2 keyboard - $5
4.Elbox right angle pcmcia adapter - 45.95
Total $338.85 plus shipping costs