Someone elses and keep yours nice and shiny
The best ones are expensive but you need to think what you want to or think you may use them for. The main thing you will use is a cordless drill.
There is a lot of decent priced stuff around but stick to better known brands. Makita, Bosch, AEG/Milwalkee, Dewalt etc. The cheaper stuff is cheap for a reason.
Try to get something with metal gearing and a metal chuck on it.
Higher amp/hr batteries mean more torque (power).
Don't be fooled by the hype over Li ion batteries. They are much more expensive, not much better and sometimes worse. Ni Cad are fine to begin with. Go for a higher amp NiCad battery rather than a less powerful Li ion and you will get a better tool for the money.
Lower voltage drill drivers (combo drills) 12 or 14v are fine for everyday use. They are light and easy to handle, have more than enough power to drive any screws you will ever use and will drill 6 and 7mm holes for rawlplugs no problem and will drill through wood whatever size you need (if you are drilling a lot use a corded and don't try to drill with 117mm holesaws on a cordless).
The heavier 18v drill drivers are too heavy to handle for doing a lot of screwdriving and their extra drilling capacity is not really worth the extra money when you can't afford it.
You won't use a circular saw too much unless you do heating installs and then a cordless one is like a chocolate ashtray. Useless.
A cheap jigsaw (corded) will do you for a while.
Get a cheap SDS corded drill. It will have more power than a 24v cordless.
Look for tool shows and demo days and ask at your local tool shops. Don't be shy to ask for a demo. They will do it no problem.
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You will probably end up spending many 1000's on tools over the years but starting off is hard.
Happy hunting.