This is something that is not written about yet as an answer and is well kept secret. There are really only 2 top companies that produce GPS maps and every GPS manufacture like TomTom, Magellan, Garmin, Newelectronx, Motorola, etc purchases there GPS maps from them. Each company may have different contracts with these said map companies and offer free map updates or not. Maps generally cost 80 to 100 dollars if they need to be updated, yet I know, it is practically the cost that you paid for the GPS. As ridiculous as this may sound, it is firmly true.
Most GPS maps are updated 2 times a year. At that time you have the option to contact your GPS manufacture for their map update releases. If there is a fee associated with the update then you will have to pay it and then maps are released to you to install into your GPS.
Most GPS models that sit on the shelf in your retail store are not up to date. Most stores purchase there GPS from the manufacture and have them sit on the shelf for some time before they are sold therefore, most will have pre-dated maps that will require an immediate update. Most second hand sellers like eBay and Amazon also order their devices from the manufacture - again, you may not get updates or current maps on that said GPS. So, check with your GPS store that you decide to purchase with before you buy a GPS. Ask the store if the maps are updated and the last time they were updated, and if there is a cost associated with new maps. You will be amazed at how many companies you will not buy the GPS from with these simple questions.
A better route to go is to get a newer GPS that is not continuously robbing you of your money, but giving you (the user) the power to what you need. You said you need to maintain the most up to date maps for you and your construction inspection job - right? Well, what better way to do that than with a GPS that will allow you the ability to enter addresses, places, and sites - if they are not already pre-loaded on the maps inside of the GPS. Also you will need a GPS that can share this said information with your computer or other GPS units, right. For instance if you cannot visit a place and your colleague at the credit union can then you can simply download or copy the new sites that you have programmed in your GPS to that colleague. This way everyone in your credit union maps will stay up to date. Seriously really, who do you know that has a job like yours that can wait for 2 times a year to update a GPS without going crazy. It sounds like you need your GPS on the go and you will need to have these locations available under your finger tips; and at will. Well, the newelectronx gps model gives this power to you. Not only does it maintain up to date maps for free. at least they were free last time i checked and that was 2 weeks ago. LOL.
Anyways, this GPS will allow you to create your own library of addresses if they are not currently programmed into the GPS.
I would strongly recommend that you go to newelectronx and look at a model called primo - 50 style. It appears to have all of the features that your question is asking for. I did some research on the company Newelectronx and you should too before you consider purchasing from any company, not just them ;). I have found that they are approved to receive paypal, moneybookers, and google checkout and they have been recognized as an online merchant for almost 10 years - therefore your money is protected. I had to make sure they were legit before i spent my money there. Did not want to be scammed; and I was not, so that is why i am recommending them to you and their GPS to you, because i know the gps quality is beyond imagination. In fact the gps will give you the ability to drive, store addresses, play MP3 songs, adobe flash movies, store pictures, bluetooth, games, and all sort of extras. It also comes with an SD card slot. This is important because most gps models do NOT have this. The card slot should turn your GPS into an address central station for updated maps.
Hope my suggestion helps you in some way or helps you get on the right track with the GPS that you can use for your job. Best of luck to you.