Welcome!
As others have said, it's really hard to say if it's possible for you to get to a size 4. We don't know your body type or frame. Also, sizes vary so much from store to store because vanity sizing is more and more prevalent.
You don't need to spend a fortune on workout things! You don't even need an expensive gym membership. These are nice things to have, but if you're just starting off, you definitely don't need it.
I don't understand the part in your post where you're talking about the dress sizes. Are they a size 10? Are they a size 4? Did you get a range of sizes?
Take a deep breath.

If you need inspiration, go visit the "Goals" section of the forum. There are some amazing women and men on here who have worked hard and made major transformations!
http://www.3fatchicks.com/forum/goal-photo-album-200/
Most people agree that diet is a bigger part of weight loss than exercise.
Look at what you're eating day to day. Is it a lot of junk/snack foods? A lot of fast food? Try to eat more vegetables and fruit. More protein. Portion size is very important too.
Will you drop three sizes overnight? No. Is there a magic quick-fix? Nope. Generally speaking, slow and steady wins the race.
3FC also has some great support groups
http://www.3fatchicks.com/forum/support-groups-122/ where you can join in and discuss your progress and obstacles with others.