I support a local school that had a "pure" asterisk box and 24 grandstream phones. they couldn't get support for the original asterisk system so i replaced it with PiAF and FreePBX. The admin like it because they can administer it themselves and only ring me when theres an issue with the grandstream phones (horrible BT101/102 phones). They have 1 BRI connected to a EPYGI gateway I put in with the PiAF server. The option for VoIP is now there with the gateway but we are waiting for the fibre before we dump the ISDN for VoIP.
You can do a similar thing with a VoIP line for say $10-15 a month, a S/H desktop and a free iso image, a selection of free soft phones or cheap IP phones(not grandstream BT101/102's !!)
Why not make it a school project ? Ask for sponsorship or similar, get the community involved. I would send you a server myself but your IT guy doesn't sound up to it. If he's a windows man then 3CX free edition is a no brainer.