So looking at hire prices they're not cheap, and the hire depots seem next to useless on advising on what gas and nails to buy. To that end is there a 'cheap' diy version I could buy?
There is just no such thing as a "cheap" trade nailer, whether you go gas or cordless. The choice is between a gas nailer, such as a 16 gauge gun by Passlode, Hitachi, Senco, etc or a cordless electric jobbie like the deWalt guns I use. Expect to spend £350+ on such a beast.
For DIY use, however, there is a lower cost alternative. Buy yourself a low-cost compressor, such as those sold by B&Q,
Machine Mart, etc then get yourself a 16 gauge brad nailer,
a low-cost one will do, a
whip hose to connect your tool to the air line, a
cheap air line (although I prefer uncoiled, these are cheaper, but they do need PCL ends - one visit to
Machine Mart or your local compressed air specialist could sort all that out) and you're away. Sometimes you'll even find kits with everything in a kit (although that is most commonly with 18 gauge guns not 16 gauge). For softwood and MDF I pretty much always use 16 gauge nails which can be had from
Amazon for about a tenner. 38 and 50mm 16 gauge should do for pretty much all your second fix requirements. If you are doing hardwood then consider an 18 gauge gun, but don't be tempted to buy a combined nailer/stapler which always mark (bruise) everything they touch. Other tools you'll need are a nail set (nail punch), hammer and a pair of pincers (Tower pattern) for handling mis-strikes