visa or not?

Hello - am preparing for my visit to Thailand.  2 years ago, i stayed 33 days & got fined for 3 days overstaying.  this time, i plan to stay around 40 days and would like to know what is the best / most convenient way to execute it?  i understand that a visa could be obtained once i arrive - for approx. US$50.00 but it would entail some sort of paperwork >> bank statement etc. which i might not have avail. during my stay in Thailand.  overstaying 10 days means 5000 baths fined - but would it cause any problem with immigration as well?  any suggestion is greatly appreciated.  david.