In reply to Jim Houghton:
Unfortunately it's a bit late now to be asking about this sort of thing.
Any competent organisation would have actually fully assessed and budgeted for the ongoing operating cost before committing to building a wall and more importantly deciding on a particular supplier. Entre-Prises walls are excellent but they are not generally considered the cheapest option.
The default option is stucking with Entre-Prises and the quote doesn't seem manifestly excessive.
Going with another individual or company is certainly possible but given that the responsibility for doing the due diligence that they are competent would rest with the school (i.e. ultimately with the head teacher) it means sticking with the manufacturer is by far the easiest and lowest risk option. Most schools I work with are intrinsically risk averse so even if a slightly cheaper quote from an apparently reputable company was obtained, there is a very good chance those ultimately responsible for the decision would decide to stick with Entre-Prises anyway.
Finally, the fact you are asking this question suggests that the school hasn't appointed an appropriately qualified technical advisor. Schools do have an exemption from this requirement under the Adventure Activities Licensing Regulations 2004 but nevertheless it would still be considered good practice.
Sorry if that all seems overly negative.