Wired backhaul will give you the best performance for the lowest material cost, if it’s feasible to run. It also lets you use simple single-radio client APs (e.g,. Groove A-2Hn) rather than a multi-radio RB, and power all APs from a central location (e.g., using one or more RB750UPs plugged into a UPS).
Other options are to connect the RBs wirelessly: either using WDS so that the client radios can double as backhaul (reduces performance), or using separate radios (increases cost due to additional antennas & radios, and more expensive multi-radio RBs).