Resolved Question: Car rental at the Shannon airport?

My friend and I are travelling to Dublin this summer from the US, and want to see more of Ireland. He mentioned renting a bike, but I'm not sure if that's a good idea. Car rentals look pretty expensive, but if they're worth it, I guess we'll have to get one. What would be the best way to get around?

Resolved Question: I'm really scared to drive in Ireland.........?

because I have never driven on the left hand side of the road. Any suggestions in how I should handle this. We need to find a car rental place somewhere on the out skirts of Dublin because I will have a holy cow if I have to drive there. Where would be a good place to rent a car out of the city?

Resolved Question: how much do rental cars cost in the UK?

my fiance and i want to hoenymoon in the UK, mostly scotland, but we're not sure how we'd get around! lol. i know there's public trnasportation, but i'm not sure how much it'd cost to rent a car, or to take a train places. we plan on visting ireland, england, and wales briefly during our 2 week honeymoon. any idea on the best way to get around and how much it'd cost?
don't know if this would help me much, but we're from the US.
thanks!! ^-^