Just a quick word of warning and I'm sure I'll have countless people that agree, but be aware of the potential costs involved in getting an old bike!
I know you said around 100 and that bike above looks by all means to satisfy your price range, but I guarantee it will end up costing you twice that in the long run.
For example, I bought a 1991 raleigh randonneur from gumtree for £80, which had been sitting for a few year but was in great condition and little used, albeit a little neglected minus the nice brooks pro saddle. (I should also add that £80 was the asking price and I didnt just go and haggle him down)
The bike cleaned up brilliantly and it seemed everything worked perfectly. However, i decided to put it in for a service as it had been sitting for a while and the tyre walls were cracked. This cost me, £60 for 2 new tyres and inners( marathon plus) , £10 for a new chain, £10 for new brake pads and £40 for the labour which included having the wheels trued and a few things regreased. £120 in total and not by any means a full service.
I then decided I wanted a new brooks pro (£90) and to upgrade to STI shifters. The chainset was also a little tired so I sourced a Shimano RSX 7 speed groupset from the forums which cost me altogether about £100 with everything except the shifters being brand new. Meanwhile, the bottom bracket went costing me another £25. I still haven't got got the STI shifters fitted but I can see now the cabling is going to need redone anyway as some of it is fraying. I'm thinking now maybe the paintwork might need redone in around a year and I have recently had to do some work on the back wheel.
ANYWAY. . to get back to my main point and not just talk about my bike, I could have at the very start stuck the bike on ebay and made an easy 300 profit as I routinely see them go for £400+ but instead I actually probably ended up spending atleast again to get mine up to a safe ridable standard.
So my point is really that although you probably arent going to want to do most of the upgrades etc I done, an old bike which is in good condition can even end up costing you loads. Even a new set of cheap tyres and a bottom bracket ( which im assuming it will most certainly need ) will end up costing you another £50, which will push you over your budget and thats of course the best case scenario as you too will probably need brake pads a chain and looks like a saddle too!
So my advice would be if you arent in it for the love of restoring ( like me and my now countless bikes that ive spent 100's on!) then either push your budget out and buy a new bike or scour ebay and pick one up which has had a service and most of the parts replaced in the last few years.
As I'm sure everyone on here know, what seemed like a cheap purchase can become an expensive hobby! Although I have spent alot of money on my randonneur, to me, it is 100% worth it, but to someone that just wants a 'cheap' bike? I'd look elsewhere.
