Depending on how long it will take to get the money.
You really are pushing shit up hill with sub standard speakers.
Id advise doing research into mixing and mastering whilst you save for a good speaker set up.
What are you using now
Headphones?
This in not a good idea at all.
High chance of permanent hearing loss with head phones. Not to mention that your mixes wont translate.
But im sure Southside will no doubt contradict me, with Fletchers Jizz on his chin.