Once every 2-3 months should be fine unless they have torn boots and are leaking for some reason. The "leaking" CV has me perplexed. Did you look at the boots? Are they torn somewhere? You should be able to replace the front wheel bearings without replacing the hub. You could do it yourself if you know how to take the front end apart. It's not hard really. If you haven't done it before then it could be fun

edit: they might be able to just repack the bearings. You also might need the whole hub, not really sure on this one. They sell the bearings without the hub which means you should be able to just replace the bearings.