Max,
Sometimes as a solo it's difficult to get a game if club or other comps/events are going on at your hoped for first choice of course on a given day or you may also have a few hours to kill before you can play.
If so don't ignore some of the second courses at the major clubs you have mentioned. Take the opportunity to play courses like the Annesley at RCD, The Bann at Castlerock, the Old or River at Portstewart. They might not be of the same standard as their famous near neighbours but you might be surprised how much interest and fun they can provide and at a price that's light on the wallet.
As to lower profile others, maybe hop onto the ferry over the River Foyle and play Greencastle, a course Jeff's often mentioned herein or maybe go further south, just into the Republic, to Greenore, which a friend of mine has frequently highlighted to me is worth a play.
Atb