I don’t think this is a din in tzaar baalei chaim. I don’t think you have any requirement to spend any money to save it (you just can’t cause it more harm). I also don’t think it’s bal tashchis because you’re are getting what you believe is your money’s worth.
In short, I think you should spend however much you want to spend, and if you decide it’s too expensive then you shouldn’t feel guilty.