just fixed my 60gb last night and all has been ok so far played burnout paradise online for like 3 hours straight after and it was fine and kinda running more quiet and cooler it seems.
i think you should attempt it yourself or get someone you know who is good with electronics and do honestly it is not that hard ,i followed the famous "gilsky" guide from youtube and also downloaded his pdf guide too in total it cost me £6 yes £6 and thats because i used arctic silver 5 thermal paste or it could have been even cheaper! but you will need a heat gun too i borrowed a mates so it was ok but you can get them on ebay for like £14 so still not bad
watch a few videos and read a few guides and get the feel of what is involved and take it from there,you will be suprised at how much crap is inside that console
fell free to come back here if you need more info or advice