the 5 main brands of most popular square filters arranged according to prices are as follows
1) tianya
2) cokin
3) hitech
4) Lee
5) Singh ray
not too sure about prices of tianya and cokin, but hitech filters cost about 60 and above , lee about 80 and above, singh ray I have never used but know of someone whose collection cost more than 1.5k.
The more common size is the cokin-p series, you will see alot of filters claiming they are compatible to cokin-p series (they set the standard cause they are the most popular

). You mentioned 4x4 (100mm x 100mm), which should be the bigger cokin z-pro which can only be gotten online (not sold in sg) or the the 4x4 lee and singh filters. Dont think tianya have a 100mm size filters.
TK seems to be the only one that sells hitech filter, cathay and TK sells Lee, cokin and tiany sold in a few shops.