All large garden costs to maintain is time, and fuel for the lawn mower, if you don’t say how big it is it’s hard to help.
Ours is three acres, it mainly laid to lawn, you can cut thr grass on the ride on in a couple of hours if you mulch it, it’s got mature beds all round it, and within, and I just get the bush cutter in there, under the soil to get rid of weeds, I don’t weed manually, and have a lot of ground covering shrubs. You need to keep on top of the shrubs, bushes and trees or things become over grown, but past that, because everything is pretty much done with machinery designed for it, I wouldn’t say it’s costly or time consuming to maintain, you need a couple of hours a week each in summer and spring, although we enjoy it so do much more, and you need time in winter early spring, leaves, dying plants, pruning etc. Basically you get a system and you chose to maintain or you choose to maintain and enhance.
I’m still not sure how you’d rent it out unless you intend to fence it off.