As Christopher highlighted, the above thread covers a lot of ground in the iOS area.
For me, it's not a question of Bias or JamUp. They are two different things. You create your basic tone in Bias then export that amp to JamUp, where it will be added to the signal chain, along with any effects you'd like.
Jim is correct, though; stuff for iOS is pricey, even if the software isn't. But if you're looking to save a little money from the start you could try an iPod touch (5th gen) rather than an iPhone or iPad. I picked one up a few weeks ago, new, for around $200. It works just as well with JamUp as either of my Ipad Minis (one retina, the other a 1st gen.). Something to consider...