In terms of cheap places to drink in Dublin there aren't many. As mentioned, there is no downtown (so stop talking about it!) but Dublin is easy to walk around. There are souvenir stores al over the place flogging the same stuff, one of the larger chains for this is Carroll's and they are in Temple Bar and have a large store near O'Connell Bridge, on the corner of the quays and Westmoreland St.
In terms of weather, last weekend was great but keep an eye on the web for weather. I'd suggest a light rainproof coat and layering options but we are heading into a late summer burst so you might be lucky
Your best options for cheaper food is to keep an eye open for early bird specials which will get you a couple of courses and a glass of wine for EUR20-25.
This is a cut and paste from previous a post on things to do in Dublin:
I am of the opinion that Dublin needs a good solid two days, one centring around the west end and sights like the modern art museum, St Michan's Church (check online for tour times as a tour of the vault is a key part of the visit), the Guinness Storehouse, Kilmanhaim jail, Phoenix Park/zoo, modern art gallery and Collin's Barracks (more likely a selection of) and a second day centrally to include the national gallery, Merrion Square (and Oscar Wilde statue), the Kildare St archaeology museum, Chester Beatty Library (in Dublin Castle), Trinity College/Book of Kells, The National Gallery across from Merrion Square, Temple Bar, Grafton St and St Stephen's Green. IMO, the Guinness factory and the Book of Kells are not worth it (particularly price wise since they are a rarity in that there is an entry fee) but visitors seem to come away satisfied from visits to both. St Patricks and Christ Church can fit it into either day. As you can see, this could easily stretch to three days. I've highlighted the places I think are the best lesser known highlights of Dublin.
In terms of good places for a few Guinness in Dublin Dawson Lounge in Dawson St, Kehoe's in Sth Anne St off Grafton St, and The International Bar in Wicklow St are all good with a bit of traditional atmosphere. Check out Porterhouse in Nassau St, near the intersection with Grafton St as an alternative to just quaffing Guinness; they serve their own brews as well as special things like Galway Hooker. There is a similar one on the corner of Parliament and Essex Streets in Temple Bar(ish).
For live music try Donohoes near St Stephen's Green (particularly Sunday afternoon session), McNeill's in Capel St (Saturday night from 9.30-midnight's great), Cobblestones in Smithfield (which might be further off the beaten track than two women might like to be late at night), and Temple Bar pub in Temple Bar (Saturday afternoon can be great but it depends on who is playing and you are paying EUR4.95 a pint). As a rule I don't rate the Temple Bar area as a late night place - pissing vomiting in the street, hens and stags - but lots of people obviously do.
Day trips from Dublin could include Dalkey and Howth (both easily accessible by train). If you are looking for somewhere to hike (or actually more like just take a good long walk) head for Dalkey by train.
I would suggest using a luggage storage place, there is one in O'Connell St called Global Internet Cafe; it is down near the Liffey end. The other advantage is from O'Connell St (up towards the other end, ehading away from the river) you can get a 16a bus for EUR 2.30 to the airport rather than the EUR5 or such that it will cost on any of the express buses. It takes a little linger.