There are 4 things in a bathroom that can make a HUGE impact on a small budget. The first two are things you can DIY making them SUPER budget friendly and the last two are things you might be able to do by yourself or you might need some help from a handy friend. Labor is where things can start getting a little pricey so do search around!
Paint! This is for sure the easiest and most cost effective way to update your bathroom, and the best part about it is you can do it yourself. And, YES you can paint your vanity. Depending on the material of the vanity you might need to do some extra work. But using an alkyd based paint is usually a safe bet for vanity painting. Benjamin Moore makes a great latex paint called Benjamin Moore Advanced Satin Latex Paint that is alkyd based. Paint, paint paint!
Hardware. Another AMAZING way to update your bathroom with very little work or mulah. At most hardware retailers you'll be able to search by style. So, depending on the rest of the style in your home you could go "modern cabinet hardware" or "mid-century hardware." You can also search by finish. Designer Tip: if you have a super "cool-based" color scheme in your bathroom (greys, whites, blues etc.) I love to bring in some warmth with brass hardware!
Lighting. Sometimes there's not enough lighting, sometimes there's the wrong type of lighting, sometimes the lighting just doesn't fit your style anymore. Whatever the case, updating the lighting in your bathroom can bring life into your bathroom. Think about what you need your bathroom floor and if you have a window for natural light. These can be deciding factors when choosing lighting. Don't be afraid to mix metals here either!
Faucets and Shower/Bath Trim. These are things like sink faucet, shower head, shower nozzle etc. Replacing these will tie in your whole project PLUS they can add bonus functionality. Better water pressure, wider spray, water saving abilities and newer technology can come with updating your faucets and trim. It's a win win.
All of these or one of these can make a huge difference in your bathroom. If budget is the biggest question do it in stages and start small. Even the smallest thing (like updating hardware) can have a HUGE impact. Also, small side note and designer tip: splurge on a nice cotton or linen shower curtain (if you have a shower curtain) it can change the whole energy of the space!