Wherever you advertise, ask for first month, last month, and a security deposit (3x rent total) before move-in. Firstly, when you put that in the ad you screen out people who don't have their shit together enough to have 3x rent on hand. Secondly, if they turn out to be flaky for other reasons, you at least have last month's rent and a security deposit. Also make sure they either a) have income equal to at least 3x the cost of rent each month or b) have some other realistic plan for paying the rent.
I'm not 100% clear on whether you're subletting a room or whether this person will be on the lease with you and pay your landlord directly, but even if your landlord doesn't require first/last/security you can still advertise that you're looking for someone who can pay that.
If your rent is significantly lower than average, you should be able to attract good roommates even with a substantial move-in cost.