Ken, like Michael above pointed out different states have different costs. In Texas, on that loan size you would have about $4000 in closing costs and should be able to get a high 4% mortgage, like 4.875%. If that will reduce your payment by $100 per month, then your break even point would be 40 months. If you are planning on staying in this home for that long or longer, then you should consider a refinance.
So, to give you the best advice, let us know what state you are in and i am sure their is a mortgage professional on this site from that state that can give you an idea of the costs, then figure out the break even point, but it does look like you should consider it.
Your closing costs can be rolled into new mortgage, so since you are at 78%, you could probably roll all costs into loan and still be under 80% so you will have no MI. If rolling the costs in takes you over 80% then i would advice you to bring some money to close to keep the loan amount under 80%.
good luck and post back with some more details.