If you have time and a little money, the most important next step is to be really patient. Eventually an exceptional deal will show up.

First and foremost, whatever you buy has to Fit you. The best bike in the world is worthless if you cannot ride it comfortably. This means you need to know what does fit---how much you like to lean, how far behind the bottom bracket you like the seat, what size seats fit .... Almost every bike you look at will be set up for someone else, which means you have to figure out how much room you have to adjust the bars, move the seat, and almost certainly the seat won't fit you ......

So you have to hop onto a bike which might be able to be made fit, and figure out whether it really can be.

If you are patient, you can wait until just the right bike comes along .... a fifteen-year-old bike might need a bit more work than you might want to do. You never know--maybe the bike was in a garage for 15 years, or maybe all the bearings are tires, the derailleur springs are weak, the brifters internals are worn and about to give out .....

Also, I don't get the impression that you know a lo0t about bikes, so it is not likely that you could identify a really great old bike from a kind of beat-up old bike which the seller polished up nicely.

Also, if you buy a used bike, not only will you have to make it fit you--which might involve buying and installing a new stem and maybe spacers, and maybe a new saddle---but you will probably want to consider new tubes, maybe new tires, a new chain, maybe brake shoes, and new cables .... which requires you to have the tools and know-how to change tires and tubes and chains and brakes and cables, and to make all the necessary adjustments ..... could you tell if a headset was too loose? Do you know what a notchy headset feels like? Can you tell if wheel bearings are worn?

There are some really excellent bikes out there for sale for really excellent prices .... and there are some worn-out, overpriced disasters which will leave a buyer drowning in regret. Make sure you get the former, not the latter.

I would suggest you go to a couple bike shops and tell people you are planning to buy a bike in a couple months when you have saved more money (so they can't get too upset when you refuse to buy a bike you don't want) and try a bunch of different sizes, different styles ....

Do you even know if you want a drop-bar bike? You might be happier and more comfortable on a flat-bar bike.

Also .... I hate saying this over and over, and last time I looked, prices were rising .... but look at Bikes Direct. BD will ship a mostly assembled bike to your home. You shouldn't even need specialty tools to assemble it ... but you might want to make cable adjustments (check out the millions of how-to videos on YouTube.) These are no-name frames with decent parts, and they are new, which means you won't accidentally buy a bike which needs a few hundred dollars of work. Also, if the bike completely doesn't work, you can send it back for a nominal fee .... but if you go to a couple bike shops to get a better idea of what you want .... then you can buy it for less online, possibly.