Yep, good monitors make a big difference. Use the search feature to track down other posts that cover monitors. Lots of info on several brands.
Also, I know you said money is an issue, but about how much do you plan to spend? Would you rather have active or passive? Active have the amp built in, passive require a separate amp. Personally, I have Tannoy Actives and like them. They are good for around $600US. If you have more money to spend there are better ones out there for sure. Also, if you can get to a music store, compare all the monitors in your price range by listening to a CD you are familiar with through them. You want monitors that sound good, but make sure and get ones with a very flat response. That way you can better judge what something really sounds like when using them to mix.