A multi choke sporter would be your best bet. Set up to be suitable for a day on clays or a walk through the fields. These guns are a balance between enough heft for multiple shots on the clay range and just light enough to carry in the field over a days shoot.
If its mainly clays you do then the O/U will a good choice, not to say a side by side won't burst clays. The issue can be its orginal intended use and build. A light weight sxs orginaly built to be carried over many miles and fire only a few shots can be uncomfortable to shot in a clay pigeon senario. Although these guns are built to last and fire tens of thousands of cartridges ovet thiet life time they weren't intended for days on the range fireing long shot string which can potentially cause problems.
Side by sides in the general shooting public have fallen out of favour over recent times. Even the traditional British driven shoot or Grouse moors are seeing a lot more o/u being used. Shooting articles have blamed shooting schools and clubs wete the go to guns are o/u. I would also say the decline, to a degree of actual hunting has a bit to do with it.

How much to spend?...... .....how long is a piece of string? How much do you want to spend? A couple of hundred euros or a couple of thousand and upwards will get you a nice gun. You will pick up a fixed choke o/u with double triggers for little money as these are now considered older technology (or you may buy one of the more desirable brand names in the same bracket for a small fortune). The market now has newer brands or old even well established brands that have entry level guns that can be bought new at reasonable prices. Are they built to last, time will tell. Some of the new entrants to Irish market didn't get a good rep in the beginning but thete seems to be evidence of a better standard of quailty control now.
What I would say is that there have always been lower end market models for sale for decades, often referred to as farmers guns. Today there are still thousands of these older guns still in use. They were often massed produced by compaines such as BSA, Baikal, Manufrance etc who's manufacturing out put was not always firearms let alone the sole production of shotguns.

If you shooting clays in a social setting then ask your fellow shooters for a go of thier guns and get a feel for what you like and what suits you. Certain brands can be short stocked or long, heavy or lite, low comb or high and unless you can afford a fitted gun or and adjustable stock then you will have to get an off the self model that suits. So shoot as many guns as you can and you will come across something you like.

Another point to consider is a single trigger versus a double trigger. If one trigger fails to function you at least have one to be going on with. The day is not totally wrecked.
If for some reason the trigger mechanism in a single trigger shotgun fails you are bunched. As others before me have pointed out if clays are your primary an O/U is a more suitable choice.