The investment depends very much upon your time and your local petshop profit margin! You need a 5.0 UV light that is positioned correctly. Check the distances from the chameleon to the light, bearing in mind that UV light loses its strength logarithmically and not in a straight line. In other words, at 30cm from the UV light you will get one reading but by the time you are 1 metre from the light you might as well not bother. This is a common mistake and cause of MBD. (There is a chart of distance and strength in my book, see below).
Ideally, use the sun ( with a UV light as a 'supplement'). If you are able to put the cage (netting and not glass) in the sun for a couple of hours a day it will be of great value. Even 4 or 5 hours at the weekend is superb. Obviously, common sense is required re over-exposure on hot days, wind on cold days, care regarding dogs and cats etc.
Basking lamps are a point of contention. I have never used them and had over 100 chameleons at one point and have raised hundreds of young veileds and dozens of panthers and carpets. But - all of my chameleons (from 4 to 6 months old) were kept outside as much as possible. If you do use an IR bulb be very careful as it can and, in many cases, does burn the lizard. Aside from MBD, burns caused by bad positioning of an infra red light is one of the more common problems seen by a vet. Check that the chameleon cannot climb anywere near it.
So - how much is your investment? Theoretically, only 5.0 UV lamp and ballast.
How long? Another point for discussion. Some people set their lights and heating to run for 12 hour cycles, 365 days a year. This is unnatural and you should aim to vary the cycles with seasons. Having said that, if you vary the temperature (and Veiled will not like 30 -32c for 365 days a year) you can stick at 12 hour cycles as the outside light will add some variation.
Hope that helps a bit. Shop around for lights but buy well known brands.
David
http://www.sa-chameleons.comhttp://www.mantispress.co.za regarding the book