Like others have said, seeing if you can work in exchange for lessons is a great idea. Getting an easy/simple job such as babysitting is a great way to make some money. It usually pays well too. You could see if there are any other barns that would pay you for working.
Sell manure. Offer to clean stables. Ask your trainer if you can help feed up, tack up or do basic barn jobs for money
I help at a barn nearby my house. That way I can buy my tack.
I work with animals, but if you want to make quick money you could always do baby sitting or something like that. You could also your at your barn to pay for the lessons.
See if your trainer will allow you to work in exchange for some lessons!
If you have the stuff enter cheep competitions that pay good money