First of all, whilst the wording of Motions on the Agenda for your AGM may be amended so long as their intent is not altered, they can’t simply be rescinded; the Meeting must resolve each Motion in the affirmative or otherwise.
Your Secretary is asking you to take on her role or that of your Strata Manager by expecting you to obtain quotes.
Why not just reword your Agenda Item to something like “That competitive quotes be obtained for the purchase and installation of ……., and that the installation should then proceed provided the total costs do not exceed $……..” ?