Nah, don't get a bandolier sling, they slap around too much, just when it seems you need to be steady and on target too! A 50-55 round over the shoulder bandolier is an excellant accessory though!
Dump the whole $250.00 if you have to and have Ghost Ring Sights put on it. It should not cost that much, but if it did, so be it! I think they are that important.
Assuming you have some money left over, a Sidesaddle would be nice as well as a cheekpiece/shell holder made by Eagle. It all depends on how heavy you want the shotgun to be, you have 8-9 rounds in it, 6 in a sidesaddle and 5-6 in the Eagle-thing, it could get pretty heavy, but that is for you to decide. That is abouit the best way to have "On-Board" Buckshot & Slugs...
The SureFire can sure be an advantage sometimes, but I would opt for the Ghost Ring Sight first off...