Well I use the Logitech G27 which has a 3 pedal configuration (Clutch, Brake and Accelerator) and a 6 speed H-Shifter. Fantastic for OMSI as you can use gears 3 and 4 on the Shifter as Handbrake apply and disengage and you've got 900 degrees of rotation that make driving a bus in OMSI have a very realistic feel. The G27 is great for other games as well such as ETS2 and ATS, as you can set up manual gearing on your truck and set the shifter to go through up to all 18 (Which is the max a truck has).
The problem with the G920/G29 is that by default it does not come with a shifter (Having a new style shifter will cost roughly an extra £30/£40), but it does have far more buttons than a G27 and is a lot quieter, which are about the only differences between the 27 and 29. Although G27's are no longer available to buy brand new, there are still a few left for sale on ebay for about £150 and having a G27 is becoming increasingly rare (I'm lucky to have one as people are just buying them and stripping them down for parts).
On the £50 you have, you can't go wrong with a Logitech Driving force GT. It does not have a H-Shifter, but does have a simple Gear Up/Down control on the side of the wheel. I believe the DFGT does not come with a clutch pedal either (Which to be honest is not to important for OMSI, not even I use it) but is a problem if you want to play other games such as ETS2 as although you can have manual gearing without a clutch, it doesn't feel right. I think save up some more and try and shoot for either a G27 on ebay or a G29/G920 (IDK which is compatible with what). However if you are not able to save up much more or are really desperate to get a wheel, then DFGT is where you should go.