What are the times and costs involved in assembling a rideable bicycle from a salvaged frame? Let's assume I bought a frame for XXX eur/usd/gbp. It usually is a steel frame from late '80s/90s, or an aluminium frame from the early '00s.
The frame is of decent quality, it does not present relevant damages and it comes with a working bottom bracket and headset.
How much time&amp;money (parts cost only) are needed to build a complete bicycle out of it?
A little definition of specs: the bicycle should have some kind of general use, i.e. running errands and short tours, so I foresee assembling it with mechanical rim-brakes, average 2&quot; tires (the frame itself may have 26 or 28 or whatever size wheels, 32 or 36 spokes according to what it can be found cheaply at the scrapyard/ bike co-op), average 3 x 8 gears. Optionals: mud-guards, hub-dynamo, rack.
Ideally, the answer to this question will be the default answer to question like:
Muddy Fox Pathfinder 90s MTB and it should not include specific products recommendations, but it should make self evident that one has to rationally compare the frame acquisition costs to all the successive costs (considerations if XXX is too much are then left as personal, opinion-based, evaluations).
ps: I do not exclude writing myself an answer in the (not so) near future, although I imagine a collective, community answer would be very nice: please don't race to answer.
This is the classic &quot;how long is a piece of string&quot; question, where almost any answer is valid.

At one end you have a frame.  And enough skills and time to assemble a bike, along with the desire/need.  If you can source every part you need from your spares boxes, then the cost is nothing more than your time.

On the other end if all you have is a frame, then every other part needs to be sourced.  Subject to finances and availability, you might be scrounging through auction listings and waiting for the right parts to come up, or you might simply purchase the parts new from a LBS.   Here the costs could range from &quot;minimal&quot; to &quot;extreme&quot; to &quot;costs more than a new bike complete with warranty&quot;


How far on that slippery slope you go is completely up to you.
A competent mechanic could assemble a bike from new clean compatible parts in an hour or two.   If you're working to mate up dirty worn and possibly incompatible parts, then the time component will naturally grow.
If you put a dollar value on each hour of your time, then the balance of the entire equation changes.
Personally, I enjoy making a bike better, so to me that's relaxing time, more productive than watching TV.

Tools  Bikes need some special tools for different tasks.  While most assembly can be done with basic tools like hex/screwdrivers/wrenches/etc, you may require more custom ones like cone spanners, cassette/freehub tools, BB tool, cable cutters, nipple drivers etc.  Buying serviceable tools is wise, they will last for life and you likely need these tools again in the future.  But that's also an added cost.
Many cities have &quot;Bicycle Cooperatives&quot; of some sort.  They may offer fixed up used bikes for small cost, or access to those tools along with expertise and advise.  Use a search engine to find the ones near you, or ask around.

Ultimately noone can tell you if something is worth doing. 
IMO if the bike can be made rideable and safe, its worth doing.
Fixing a bike is it's own reward.