It depends on a lot of factors. First, whether you are getting a made to measure suit, or bespoke. A made to measure suit is made from an existing pattern, that is adjusted to the customer’s measurements, and can often have details, such as lapel, and pocket styles, changed to his preference. A bespoke suit is made from a new pattern, that is drafted specficallly for the customer. Bespoke is both more expensive, and more time consuming.
As to price, it varies widely depending on whether it’s MtM or bespoke, what type of construction you go with (fully canvassed, half canvassed, fused), some of the details, where you live, what fabric you choose, what tailor you go to, etc. Timing can be anywhere from a few weeks, to almost a year, depending on which route you go.
Online made to measure suits are often problematic; they’re the sort of thing where yu really need to know what you’re getting, and what you want, in order to assess whehther it’s a good value. Two good places to ask (where many people are knowledgeable, but not all, of course) are styleforum.net, and the forums at askandyaboutclothes.com – there are also many blogs, and sites with information about this.
Custom suits are not necessarily better than ready to wear, and they (made to measure especially) will not necessarily fit better. To be a good fit, made to measure suits need to start from a pattern that already has the right general shape for the customer, so they are not necessarily going to be any better than a properly fitting ready to wear suit, after alterations. The biggest advantage to made to measure is usually control of the material, and details.