Isaia can be a bit confusing with regards to their different lines. They are as follows:
Enrico Isaia - Top of the line, hand made and expensive. I have never actually seen one in a store in the US.
Gianluca Isaia Napoli - Excellent, and every bit the quality of the better known names. I only own an few of the ties, though I have seen the suits and they are lovely.
Isaia Napoli - This is the one with the red tag, and probably what you will find if you are looking for discounted gooods. Lots of hand work and top quality. Readily available in most big cities (Neiman Marcus and the like as well as independants such as Boyds, Stanley Korshak, etc. carry these). If you are patient (some of the cloth is a bit wild for me), this line is often at outlets, STP etc. Retail is generally in the $2500 - $3000 range, though as mentioned above, discounts can often be had. These are very well made suits and an excellent value relative to other Neopolitan makers, though you do have to have the right build for them (at least the ones I own). Though the sizes are true, the cut is one of fairly high arm-holes, slimmer pants and fairly low rise compared to what you may be used to if you are new to Italian suits. Just make sure you go to a brick and morter retailer to try on, or buy online from someone who allows returns for your first suit. For reference, I am 6' 185 with 34 waist and the 52 with 8L drop (US 42) fits me almost perfectly off the rack.
Note that this line used to have a grey and black label (similar to the Gianluca Isaia Napoli line) until about 3 or 4 years ago.
Gianluca Napoli - This is the diffusion line, mostly machine made. I have no experience with it, though it is not too well regarded on this forum. I suspect that may be in relation to the other Isaia lines and not necessarily to other makers at the same price point, but I don't know. Regardless, don't get confused with it and the high-end Giancaluca Isaia Napoli line.
Note that all of the above (with the possible exception of Gianluca Napoli) will not come with finished sleeves. Therefore, be careful of one that is finished as it will have been altered for someone, and once the button holes are cut, you can't just move them like the non-working sleeves. Alternatively, if you don't have a tailor who will cut the button holes, try Paul Winston at Winston Tailors in NYC. He is a contribution to this forum and does a good job at reasonable cost. I just have my tailor to the alterations but leave the sleeves unfinished and send it off to him for finishing.