If it's in a good condition, real Shimano 105 parts, not run down too much, not rusted, all working and decently maintained then it might make sense. But if several parts need replacing then you can easily pay another $200 or more for just bringing it to working condition. There are many roadbikes available on ebay or so within that budget, compare your options. Go for something in a good working condition, or get some bike mechanic to check it out for you.