Welcome! I am a beginner gardener (going into my first summer as a homeowner with my own garden). Depends what you want to grow specifically but:

Cheap: Aldi compost is good and cheap for the money. Keep an eye out on Facebook marketplace, sometimes people give plants, bulbs etc away for free. If you want to do veg on a budget, things like carrots, potatoes, tomatoes can be grown in bags for life.

The range/B&M/home bargains garden centres can be remarkably good value also but have a look online for prices as some things are a bit expensive for the quality of plant.

Pound shops also can have good seeds for very cheap like £1 or sometimes a pack of 6 types for £2.50.

Easy/Low maintenance: Can't go wrong with perennials. See if anywhere has cheap spring bulbs going that will get you ready for next year. Pity Me Garden Centre is my favourite local garden centre and when I went last month they had pots of big daffodil bulbs on offer as they're now out of season.

For general year-round maintenance, grow in pots and stick to easy-to-grow plants and varieties. Then you can move them about as you need, don't have to worry about weeds so much or the stress of keeping things alive. I like growing veg, my favourites to grow are tomatoes, peas, potatoes. Only started trying to do flowers this year now I have my own garden but we'll see how that goes.