It sort of depends on what you mean by reasonably priced! If you think about it 1st fix nailers in particular have to be pretty robust to survive the constant shock loads they are under. They are also a relatively low volume product in comparison to, say, combi drills (TBH I can't see many electricians or tilers needing a 1st fix nailer) with most buyers being trade and requiring reliability over price. So they tend to be expensive.
That said, I think there are two possible alternatives:
1. Small portable compressor (under £100), low cost filter/regulator (£20), fittings and hose (£30) with consumer grade pneumatic tools (e.g. Axminster, Clarke, etc - Ryobi do sell a better mid market product range in the USA with grey imports often being available here)
2. Ryobi AirStrike cordless tools (cue
@big-all )
Unfortunately I can't give any personal recommendations on specific tools as I just don't use them
I do have some limited experience of low cost pneumatics and all I will say is that the first fix guns aren't much good for the sort of volume work I do (e.g. up to 10k 50mm ring shanks in a day, etc) but they can do lower volume stuff. I have in the past used low cost 16 ga and 18 ga 2nd fix nailers (Rockwell, an old B&Q house brand) as stop gaps when my main pneumatics were on the bench and neededvsomething urgently. I had no problems in short term use. Air tools are actually pretty reliable requiring only a bit of air tool oil before each usage session and being kept dry, clean and oiled between use (so don't store in a cold, damp garden shed over the winter - if only because the aluminium used in their construction will oxidise)
The Ryobi cordless AirStrike tools are available in the UK and are probably the only worthwhile readily available mid market pneumatic tools around, but they are aimed at the home worker market and are not as robust as, say, Senco or Passlode. But then they cost a lot less. See AvE on YouTube for a strip down video on one of the Ryobi Airstrike tools
As to the sizes of tools you are looking for I'd suggest that you look for a clipped head nailer (these use paper collated, clipped head, 30 to 34° nails from 50 to 90mm long), whilst for the 2nd fix I'd suggest going for a 16 ga gun as these take 32 to 64mm nails, as opposed to the 25 to 50mm of 18 ga guns. The 16 ga holes are bigger than 18 ga, but you get better holding power with them and in any case on painted work it makes little difference once you've filled them