Where to start

Define your garden- What type/style (see some types listed below) look in magazines, notice other people's gardens, books and online . This can help you determine what style you might like.

Pollinator Garden, Native Plant Garden, Mixed Garden, Ornamental Garden, Reduce your lawn, Low maintenance, Water Conservation, Edible Garden, Tea Garden, Secret Garden, Fairy Garden, etc.  The ideas are endless.

Pick an area in your yard.  Start small so you do not become overwhelmed

Know what you can realistically do on your own (don't forget the tools, knowledge, skills, physical ability and time available to do it). Gardening is a lot of physical work and time.  If you don't love doing it you will have trouble motivating yourself to do it.  Even people who love to garden, don't enjoy pulling weeds. (don't worry there are strategies to minimize weeds).

Things to think about to plan and budget for:

Determine how quickly you want to see results (if it's quickly, it will cost more, if you can wait a year or two (for plants to mature from seeds),or a combination: grow perennials that will come back every year although they take a 1-2 years to mature ( and tend to be lower maintenance, and fill in with annuals that are grown from seed or buy plants(annuals only last for the season). 

You can also save by trading plants with friends or neighbors, garden club sales, etc.  (just know that you must check the roots and soil and plants carefully for unwanted guests.  Examples: unwanted invasive plants, invasive jumping & snake worms.  You don't want to spend years trying to weed out an invasive hitchhiker.  They hide easily within the plant or roots. So be sure to check carefully.  I made this mistake years ago in my early gardens.  Invasive non native plants are very hardy and hard to get rid of.  

Remember to think about materials needed: soil, seeds, plants, borders, sprinklers, soil test.  Fit the plant to your garden conditions. Think right plant right place and make your gardening easier.

Divide your project into segments/seasons. Use the best conditions for plants/seeds and segment your garden by those conditions/seasons. 

This will help you get optimal results from your plantings and spread out your expenditures. Planting your trees and shrubs in the fall will give your the best results, when the conditions are best for them to work on their roots and prices are at their lowest for these.  Seeds and small perennials do best in the spring being planted in the spring.  Plant dormant early spring bloomers in the fall.  

Good seeds cost approximately: $3-7 per packet (not including shipping),  a small 6 pack of annuals(last for only 1 season) can be $5.99-9.99, larger annuals $9.99+ per plant.  Small Perennials (last for many years or self seed)$5-$12 per young plant, $16 + for 1year old plants.  These are estimate of good quality plants from local small native plant nurseries.  Try to avoid buying plants from a store that doesn't specialize in plants.  Remember you get what you pay for and they usually aren't a good quality and don't receive good care while waiting to be purchased. 

With this knowledge you will have a good place to budget and plan for your garden.  I hope this helps you avoid some surprises when you begin your gardening experience.  It will be worth it.