The cheapest paint job as far as I know is DiY.
I tried doing my own repaint and it's a very tedious and time-consuming process if you don't have the right knowledge, the right tools and the right skills. I did the lazy way and left everything intact while I did the stripping of the paint. I didn't do a re-spray but simply stained the body with a wood stain. The stripping of paint was the hardest as I did not have a sander to remove the old paint. So it was all elbow-grease and hand sanding with lots of sandpaper. I can tell you it's very messy. And very tiring.
Hence, I now understand why it cost a bit to do a repaint of the guitar. There is so much work involved and very time-consuming. So if you want a professional re-spray, it wouldn't be worth it if your guitar is a low end one. The paint job will cost more than the guitar.
A place where you can do a re-spray is Guitar Workshop at Bras Basah Complex. Same level as Swee Lee, behind Art Friend.