Re:
If you want to buy a nice frame quickly and cheaply then you could do a lot worse than a Merckx Supercorsa. Available for £300 to £400 on eBay or a bit less on LFGSS.
I have a '98 model in a very 90s purple colour scheme, kitted out with 9sp Ultegra of the same (roughly) period. It's the nicest steel frame I've ridden and I had a custom Bob Jackson (which I really didn't rate) at one point. It weighs 9.5kg. More modern parts and (especially) high end wheels would shave a kilo off that.
I'm only 63kg and ride a 55 so frame flex is not really an issue for me. This puts me off modern steel frames with their massive downtubes and chain stays. I think the builders are moving too far away from what makes a steel frame desirable and are just making aluminium or carbon inspired frames which have the ride characteristics of oversized aluminium - stiff, harsh - but with a weight penalty.
I also have a modern Canyon carbon fibre frame with Campag Chorus and tubeless tyres. Very modern, very light, stiff yet comfortable and great handling. It's different to the Merckx, rather than being nicer or not as nice. I ride both equally, depending on what mood I'm in.
I have a significant birthday next year and my present to myself is likely to be a Tommasini Tecno in slightly oversized Nemo tubing, or another Genius / Nemo frameset with modern parts.