Ultimately, if your objective is to have a clean business - everything recorded properly - you'll have no choice but to pay the VAT. As far as legality is concerned, a VAT-registered business that offers to sell you goods or services without issuing you an invoice/official receipt is breaking the law. Look in any major store, for the orange Notice from the BIR posted somewhere near the cash register. Read it carefully.
That being said, it's a fact of business in the Philippines that many establishments document sales with Delivery Receipts. That way, the sale is off the books. The advantage to the seller is that, well, that income isn't reported. The advantage to the buyer is, no 12% VAT. The disadvantage, however, is that the buyer is unable to legally record the purchase in her books. That is, you spend cash from your business, but you can't legally record that expenditure. So, in the eyes of an auditor, that cash must STILL be with you.
Of course, you can record the purchase anyway, and indicate that you were issued a DR. This can cause all sorts of trouble for you if you're audited, and it will cause even more trouble for the seller - remember the orange notice? Especially if you paid in check form, there's evidence that money flowed from your company to the seller, and the transaction isn't on the seller's books.
You'll notice that large companies will never do this. I believe there is a BIR directive, that the top n corporations (I don't know the number - 1,000 perhaps?) actually WITHHOLD a portion of the amount paid to the seller, to be paid directly by the buyer to the BIR. This is essentially an advance tax on the seller. The effect of this is that BIR has a record of the sale transaction, which they can use in auditing the suppliers of large companies. Since you're starting, you're still under the radar, so to speak, so you may be tempted to take the DR route.
As jessica jinky panes points out, it's a non-issue if you're VAT registered. The way it goes, you collect VAT for anything your business sells. You in turn pay VAT on anything your business buys from VAT-registered suppliers. The VAT you collect, less the VAT you paid, is what you remit periodically to the BIR. It would therefore be in your best interests to buy from VAT registered suppliers. Since you're not VAT registered, basically you lose out on the VAT mechanism when you purchase from VAT suppliers, like in your case. However, you may one day get big enough (and what business owner doesn't dream of that day?) that you'll be REQUIRED to become VAT registered. Any business can choose to become VAT registered at any time; but if your annual gross sales exceeds - I think it's P1.5M - you will be required to register for VAT.
