Who cares OP?! I mean, seriously. who cares what other people think? What is important is you when you're running, not what anyone else thinks. That said, I doubt anyone will notice you anyway.
I'm a runner, and in the unlikely event I look at someone else out running, I don't make judgements on their running style. I must admit I might briefly think about whether they're faster or slower than me, but that's the extent of it! If I see someone really large out running, and I mean by that perhaps over a size 20 or so, I would think nothing but really admiring thoughts about them.
You will probably find that running makes you more self confident and more likely to feel like twatting someone that gives you any negativism.
That said, you might get abuse shouted at you, but ignore it, develop a thick skin. I'm a size 8 - 10, and I get it. We live in a country where abuse gets shouted at women on their own. I was on holiday in Turkey recently, and thought I would get hassled while I was running alone, but actually it was fine, and so refreshing not to be shouted at by groups of children when you passed them.
btw when I was larger boobed, by far the most effective thing for keeping them from bouncing was wearing a tight fit racer style swimsuit underneath instead of a bra.
I spend £70 - £80 on trainers and they last me about 6 months.