Budgie Sneezing Fits

Hi all.
So we have had Flynn for about 2 months now. We got him from a breeder at about 7 weeks of age. About 3 weeks ago, we started noticing that Flynn was having more frequent sneezing, to the point where he would have sneezing fits - continuous back to back sneezes, about 6 to 8 in a row. This eventually started getting worse, where he would have back to back sneezing fits - three sneezing fits of 6 or so sneezes back to back .... the poor little thing!! We did notice that he seemed a lot more lethargic and was sleeping more... but his droppings were normal, there was no fluid from his beak and everything still seemed okay.
We took him to the vet last week who said that he possibly had some sort of bacterial infection in the back of his throat and gave us some antiobiotics to give to him twice daily, into his beak. The vet said Flynn had about 10-20% bad bacteria which was assessed from his throat/dropping sample (budgies normally have about 2% bad bacteria), so he said this could possibly account for the sneezing but he seemed a little surprised it wasnt a higher percentage. He said Flynn also had "budgie boogers" - staining about his cere which indicated he had been sneezing quite a bit. The vet told us about chlamydia and asked us to test for it but we declined as the test was an extra $130!! The vet said that if Flynn didnt improve then he possibly did have chlamydia. However, Ive been reading about chlamydia and there seems to be a lot of other symptoms that go with it in addition to sneezing!?
Anyway, we are 5 days into treatment. I have to say after about day 2 we noticed a huge change in Flynn's behaviour - he was much more active and playful. Previously he would fall asleep around 7.30 or 8pm but on day 2 he was playing with us well past 9pm! I have to say that this improvement seems short lived though.... over the weekend Flynn had a sneezing fit on both saturday and sunday - about 6 to 8 sneezes in a row again, but it wasn't back to back fits like before (could this be considered an improvement!? i don't know!??). He seems better than when we initially took him to the vet but I don't feel that same level of alertness/playfulness that we observed on day 2 is there. So Im a little worried that these antibiotics are a short term solution and not going to get rid of the issue 100%. Flynn still has staining above his cere as well - it seems to have reduced a bit, but it is still present.
I just wanted to ask if anyone out there has had experience with something similar before and if they have any advice??? I guess at this point I need to finish the course of antiobiotics and even though I may be getting ahead of myself, I am a little skeptical that it is working as the vet said we would "almost have a new bird" after several days into treatment!
I don't think we will take him back to the vet to be honest for financial reasons.... the first bill was $200 and I guess if he doesnt get better and may have chlamydia, then the 6 weeks intensive injection course is going to be very expensive!!! I have been reading about raspberry cordial and how it can do wonders for sick budgies but Im wondering if poor flynn may be a bit beyond this stage!?? Any advice/info would be much appreciated!! Cheers!