You have a few options.
1. ASEBA-Web works on a system of e-units. Each form you send out costs two e-units, and you can see the price of additional e-units here:
A full explanation of ASEBA-Web pricing is available here.
The primary advantage of ASEBA-Web is that it provides informants access to a site where they can fill out the forms themselves. This may save you considerable time and avoid data entry errors since you won't have to key-enter the forms one by one.
Another advantage is that you can access ASEBA-Web from any device including Macs, PCs, and tablets.
Additionally, ASEBA-Web is that it gives you access to form protocols from all age groups.
2. ASEBA-PC 2015 requires at least Windows 7. It can be only be run on a single machine per license, though multiple people can use that machine. Licenses are sold by age group, but there is also a full-set option that gives you access to all age groups.
3. ASEBA-Network 2015 runs on a server on your network. Multiple people can then access it simultaneously from any computer with a modern, up-to-date web browser. Similar to ASEBA-PC 2015, you have to buy access to specific age groups or purchase a "full set" license. You can see the installation requirements here: http://aseba-network.aseba.org/