Ok, plannig a trip for May. Trying to figure out some things.
One opion would be to fly into Ireland, stay a few days, fly to Edinburgh, stay a few days, and then rent a cottage for a week in Scotland and drive all around.
We are trying to figure out if it is really worth it to just spend a day or two in Ireland before spending the majority of time in Scotland and would the airfare to Edinburgh from Ireland be very expensive.
Still trying to find the best flight deal from US and have seen some cheaper flights into Ireland and then we could take local service from there.

Try Ryanair for discount fares online,some February dates now going for 3 euros + airport tax.
Or fast ferries:
troon-belfast Seacat
cairnryan-larne P&O summer only
stranraer-belfast Stena

You can find very cheap airfares from Irel;and to Scotland - but for only a couple of days I'd recommend spending the whole time in Scotland.

If you can find an amazingly good fare into Ireland - then OK, it makes more sense. But you should also look for fares into London or Manchester. Sometimes you can get better fares into London than into Ireland and then fly/train/or drive up to Scotland.

I sometimes fly into Manchester and pick up a rental car there. The drive up to Scotland is easy and would let you visit the Lake District and/or Hadrian's wall enroute.

Agree with Janis. You can usually find the best fares into London. In May, we are flying to Gatwick, renting a car and driving up to Scotland with a stop in the Cotswolds and Lake District. We'll then fly back to London from Edinburgh (28 GBP each on flybmi.com)so we can stay in London a few days before flying home. Our round trip fare from Houston for 2 people was under $950 on American.

I booked our flights back in November when the airlines had those great sales. Hopefully, there will be another big sale before Spring.

We stayed for a week in Callendar, located a few miles for Sterling. Got a great cottage at the Leny Lodge. Big place with 2 big bedrooms, two baths, kitchen, dining room, living room with fold out bed. Was about $500 in 1999