Both the Gloucestershire schools I've worked in could buy from who even they wanted to. We have to get three quotes for larger orders.
We buy decent LCD projectors Sanyo's mainly the UX88's and the UX74's. We fit it ourselfs. Saves a fortune.
We are supposed to get three quotes but unless it is a very big job I don't bother.I am just the tech (or network manager as there is only me!) but it is completely up to me who I use and I tend to use people I have used before or others have recommended.
It would be a good idea to advertise on Edugeek, with incentives, as once one or two of us have used you and are happy, others will follow
Just make sure that you are getting the required number of quotes required in your schools financial handbook. You should have something like that which states how much the cost should be before you need to gather additional quotes. If not, ask your bursar. You may have a procurement policy.
If you have the auditors round from the council they will not be pleased if there is no paper trail or records kept of past quotes. They may think you are on the fiddle.
Network Manager or Technician, perhaps you should clarify who is actually responsible for those things when the bleep hits the fan. Preferably make sure it's the guy who actually is the budget holder.:p
Also I make sure I get the agreement of the Dep Head before I actually buy anything much.
There are no budget holders as such other than the governors and a sort of 'rough' idea of what some depts have - I say 'rough' because I get told to just buy stuff even if we are over budget and we will find it from somewhere.
Only little stuff though, never big stuff we REALLY need