What are essential funding barriers to get an ambitious and pertinent research proposal funded, and how to overcome them ?

There is no ambitious and pertinent research proposal. Proposals are normally done after needs assessment has been done. If the proposed research idea aligns with what would help alleviate a specific problem then it is not ambitious. It only becomes one if no proper needs assessment was done hence no adequate implementable research question and design (rationale), that would lead to activities and hence cost. In this regard, if one does not understand the research problem to be addressed then there is no proposal. The ambitious bit of it normally comes on the costing since one wants to cost activities that either are not relevant or does not align with the problem to be solved because one is thinking of solving a none existing problem (imaginary/superficial).  To circumvent this problem, one needs to critically understand the problem at hand, its would be impacts if solved and then development appropriate line methods to solve it.