Unless you are in a multi-tenanted building every new carrier you add will charge $10K-30K in construction fees to bring fiber into your building. If Cogent is available OnNet that is your cheapest option, they're bottom of the barrel, definitely less than you pay for 4-line MLPPP DSL and depending where your server is probably better speed most of the time too. I would stick with Beanfield personally, they are first-class and have exceptional support. Of course the slow wifi doesn't have anything to do with your ISP, get some repeaters installed and switch to 5GHz 11n/11ac if possible.